Immigration judges oversee an essential part of the system: granting asylum to migrants whose claims pass muster and ordering the deportation of those whose cases do not.

Tom Jawetz, a senior lawyer in the Homeland Security Department in the Biden administration, said the move suggested that Mr. Trump would try to insert loyalists who could undermine veteran career officials into key roles, as he did during his first term.

“Politicals during the first Trump administration ran roughshod over the career civil servants who have dedicated their lives to public service,” Mr. Jawetz said in an interview. “A Day 1 blood bath like this indicates that they don’t intend to change course now.”

As of Monday evening, there was no announced leader of the court system and the webpage that previously listed the acting director said the position was vacant.

The four officials included Mary Cheng, the acting director of the Executive Office of Immigration Review. The three others fired were Sheila McNulty, the chief immigration judge; Lauren Alder Reid, the head of policy for the agency; and Jill Anderson, the general counsel in the Executive Office of Immigration Review.

“I received an email from the justice management division after 3 p.m. that informed me that I had been removed,” Ms. Alder Reid said in an interview on Monday.

Ms. Alder Reid had been with the agency for more than 14 years. Ms. Cheng had been with the department since 2001.

In Mr. Trump’s first term, his administration sought to reshape the immigration court system by instituting quotas for judges and no longer allowing them to pause cases that they felt were not a priority. It also altered when immigration judges could grant asylum to migrants appearing in court.

“The firing of these senior immigration court officials will be a severe setback to the effective functioning of the courts which are already backlogged with millions of cases and need experienced court administrators to ensure cases move expeditiously through the judicial process,” said Greg Chen, senior director of government relations for the American Immigration Lawyers Association, which represents the nation’s immigration lawyers.

The court system has been under immense pressure for years. The immigration court backlog ballooned to more than three million cases at the end of 2024 fiscal year, according to the Congressional Research Service.

As he replaces Antony J. Blinken in the job, Mr. Rubio confronts a daunting list of foreign policy tests. They include the war in Ukraine, a fragile cease-fire in Gaza and, in what Mr. Rubio calls the century’s defining challenge, China’s global ambitions.

But perhaps his biggest hurdle will be managing his relationship with Mr. Trump, whose temperament and worldview are very different from his own. Over three terms as a senator, Mr. Rubio was known for his hawkish foreign policy views with a heavy emphasis on human rights. Mr. Trump is a skeptic of foreign entanglements and takes a transactional approach to the world.

Foreign diplomats will also closely study the relationship between the president and Mr. Rubio, given that they clashed with memorable bitterness as rivals in the 2016 Republican presidential primaries. Mr. Trump was never in sync with his first secretary of state, Rex W. Tillerson, and fired him over social media after a little more than a year in the role.

Mr. Rubio was born in Miami in 1971 to parents who left Cuba for the United States in 1956, shortly before Fidel Castro took power in the island’s communist revolution. His father worked as a bartender and his mother as a hotel housekeeper, and the family spent several years in Las Vegas before returning to Miami. Mr. Rubio graduated from the University of Florida in 1993 and then earned a law degree from the University of Miami. He served in the Florida House of Representatives, including as its speaker, from 2000 to 2008.

Mr. Rubio then won a 2010 election for Senate and arrived in Washington amid talk that an energetic young Latino from Florida could make a formidable presidential candidate. He made an early name as a proponent of bipartisan compromise on immigration and promoted an interventionist U.S. foreign policy with a special distaste for repressive dictatorships like the one that Mr. Castro imposed on his parents’ native Cuba.

But when he sought the presidency in 2016, he met a roadblock in the form of Mr. Trump, who called him a scripted Washington insider and ridiculed his stature with the nickname “Little Marco.” Mr. Rubio’s arguments that Mr. Trump was unsuited for the presidency fell flat.

But Mr. Rubio became a defender of Mr. Trump and continued to hone expertise as a member of Senate committees on foreign relations and intelligence.

At his confirmation hearing earlier this month, he pledged to take a more “realistic” view of American interests abroad. He also called for ending the war in Ukraine, expressed strong support for Israel, and said that countering Chinese power would be among his top priorities.

The name change is likely to face some pushback in Alaska, where politicians and Alaska Natives alike have long favored calling the mountain Denali. The name, given by the Koyukon Athabascans, translates to “the great one” or the “high one.”

Mr. McKinley first championed tariffs as a member of the House of Representatives in the late 19th century. He also oversaw the expansion of American territories, including through the forced annexation of Hawaii, as well as the empowerment of wealthy industrialists.

In 1896, as news spread that Mr. McKinley had won his first term, a prospector exploring the mountain range declared that the tallest peak should be named in honor of the new president — a decision codified in 1917. (Mr. McKinley, assassinated in the first year of his second term, never stepped foot in Alaska.)

The mountain, which stretches more than 20,000 feet high, has been informally known as Denali for decades and, in 1975, Alaskans began to push for a formal name change.

Lawmakers from Ohio, the home state of Mr. McKinley, repeatedly objected to efforts to legislatively change the name, until President Barack Obama used his executive power to restore the Denali name in 2015.

Both Senators Lisa Murkowski and Dan Sullivan have expressed support for calling the mountain Denali, according to The Anchorage Daily News.

“You can’t improve upon the name,” Ms. Murkowski, the chair of the Senate Indian Affairs Committee, said in a December statement, noting that it was “the rightful name for this majestic mountain to respect Alaska’s first people who have lived on these lands for thousands of years.”

“This is an issue that should not be relitigated,” she added.

Democrats on the panel had tried to delay the vote amid deep concerns about allegations that have been raised about Mr. Hegseth’s conduct. But their efforts to slow his march toward confirmation to allow more time to investigate those claims were unsuccessful.

Shortly after Mr. Trump chose him to lead the Pentagon, Mr. Hegseth faced a raft of allegations of personal misconduct, including an accusation of sexual assault and reports of public drunkenness and financial mismanagement.

During his confirmation hearing, Mr. Hegseth denounced the claims that he sexually assaulted a woman in California and had been severely intoxicated in public as “anonymous smears.” Mr. Hegseth reached a legal settlement with his accuser in the sexual assault case, which included a nondisclosure agreement that barred her from speaking about it publicly. He was not charged in the case.

Because Mr. Hegseth’s accusers have, to date, remained anonymous, Republicans refused to let them upset their push for his quick confirmation.

“All day, I’ve been hearing about allegations,” Senator Roger Wicker, Republican of Mississippi and the chairman of the panel, said Monday before the panel’s vote.

“That sort of thing certainly is not going to stop us from sending the nomination on to the full Senate,” he said, adding, “If they were substantiated and taken seriously, we’d look at them.”

Sharon LaFraniere contributed reporting.

Replacing a website that on Monday morning had been a colorful, video-rich homage to President Joseph R. Biden Jr.’s accomplishments and record, the Trump administration introduced a simpler website with a dark blue background.

As of Monday evening, the website included a rundown of Mr. Trump’s early actions in office, a list of priorities for his presidency, and brief biographies of his cabinet nominees.

The differences were stark. Gone was talk of “tackling the climate crisis,” replaced with a pledge to end “policies of climate extremism.”

Out were Biden administration boasts that the White House had “forged historic partnerships” and “restored American leadership.” In was a promise that the United States would “no longer be beholden to foreign organizations.”

“Every single day I will be fighting for you with every breath in my body,” read a message on the homepage, above a rendering of Mr. Trump’s signature. “I will not rest until we have delivered the strong, safe and prosperous America that our children deserve and that you deserve.”

The replacement of the website is a digital tradition that follows the swearing-in of every new president. Before Mr. Biden took office on Jan. 20, 2021, replacing Mr. Trump after his first term, the website carried a banner that said “Promises Made, Promises Kept” and highlighted Mr. Trump’s work to resolve the Israeli-Palestinian conflict and help American workers.

By that evening, a new, bare-bones homepage had appeared showing Mr. Biden at a lectern, hands folded, in front of a large American flag.

Robert Jimison contributed reporting.

Mr. Peltier, 80, is in poor health and partially blind, after suffering bouts of Covid-19, an aortic aneurysm, diabetes and a stroke. The commutation, Mr. Biden said in the grant issued shortly before President-elect Donald J. Trump took his oath of office, will allow Mr. Peltier to serve the remainder of his sentence in home confinement.

“If there were ever a case that merited compassionate release, Leonard Peltier’s was it,” said Senator Brian Schatz of Hawaii, the top Democrat on the Senate Indian Affairs Committee, who has long championed a pardon for Mr. Peltier. “President Biden did the right thing by showing this aging man in poor health mercy and allowing him to return home to spend whatever days he has remaining with his loved ones.”

Mr. Peltier, a citizen of the Turtle Mountain Band of Chippewa Indians, received two life sentences in connection with a shootout between federal agents and tribal rights activists in 1975, which left two F.B.I. agents and one activist dead. Mr. Peltier, part of a movement dedicated to upholding Native American treaty rights with the American government, has admitted to participating in the shootout in self-defense, but says he did not kill either agent.

“This last-second, disgraceful act by then-President Biden, which does not change Peltier’s guilt but does release him from prison, is cowardly and lacks accountability,” said Natalie Bara, president of the F.B.I. Agents Association, a private nonprofit that serves the bureau’s current and former special agents. “It is a cruel betrayal to the families and colleagues of these fallen agents and is a slap in the face of law enforcement.

Mr. Wray had also argued against granting any form of clemency in the case. And on Monday, Attorney General Marty Jackley of South Dakota said his office “strongly opposes this action and has in recent months argued against any change in the defendant’s sentence.”

In the waning days of the Biden administration, as the president granted thousands of pardons, tribal leaders and Democratic lawmakers intensified their yearslong push for Mr. Biden to include Mr. Peltier.

His supporters said that his trial was unjust, pointing to exculpatory evidence used in other trials related to the shootout that was excluded from Mr. Peltier’s. The U.S. attorney whose office oversaw Mr. Peltier’s prosecution has also joined an array of global and federal leaders, including the Dalai Lama, in calling for his release.

Mr. Peltier had parole denied repeatedly, including in July. But he remained “a leader of our people, and an elder of our people,” said Nick Tilsen, the founder and chief executive of NDN Collective, an Indigenous rights organization. “It wasn’t just about his freedom. It was about freedom for Indian people.”

Devlin Barrett, Mark Walker, Mattathias Schwartz, and Rachel Nostrant contributed reporting.

“Vivek Ramaswamy played a critical role in helping us create DOGE,” said Anna Kelly, a spokeswoman for the White House, adding, “We thank him immensely for his contributions over the last two months and expect him to play a vital role in making America great again!”

Mr. Ramaswamy’s position in Mr. Trump’s orbit has been tenuous for weeks as he irritated the president, several of Mr. Trump’s aides and, crucially, Mr. Musk. Mr. Musk has been sharply critical of Mr. Ramaswamy in private conversations.

Mr. Ramaswamy plans to announce his bid for governor of Ohio next week, according to a person familiar with the matter who spoke on the condition of anonymity because they were not authorized to speak publicly.

Mr. Trump announced the two billionaires to be co-leaders of the project, but it was an unequal partnership from the start. Mr. Musk has a much greater amount of wealth and a higher profile, and a top lieutenant of Mr. Musk, Steve Davis, largely runs the project.

Some allies of Mr. Ramaswamy insisted until recently that he was not immediately leaving his position. Mr. Ramaswamy has told others close to him that he would not begin a bid in Ohio until much later in 2025, and so he was working to explore a campaign for governor even as he remained a partner with Mr. Musk in the project.

But Mr. Ramaswamy recently came to see the idea of coleading the efficiency effort and running for office at the same time as unworkable, the person familiar with the matter said. The governor’s seat is up for election in November 2026, and officials at the advisory group are expected to offer recommendations for reducing federal spending by July 4, 2026.

The decision came after Gov. Mike DeWine of Ohio announced that Lt. Gov. Jon Husted would fill the Senate seat being vacated by Vice President JD Vance. Mr. Ramaswamy was also a contender for the vacancy, and Mr. Trump recently told him that he would be a good fit.

It also followed Mr. Ramaswamy’s comments blaming an American culture that venerated “mediocrity over excellence” for top tech companies often hiring foreign-born engineers. People close to Mr. Trump said he was unhappy about Mr. Ramaswamy wading into the online debate over H-1B visas among conservatives, many of whom saw Mr. Ramaswamy’s comments as critical of American workers.

The Department of Government Efficiency is not an official government department, despite its name. In November, Mr. Trump said the entity would provide outside advice on how to cut spending and work closely with White House budget officials.

Mr. Musk arrived in Washington for Mr. Trump’s inauguration and was seen spending time on Sunday afternoon at the SpaceX headquarters in downtown Washington, which is where most of Mr. Musk’s and Mr. Ramaswamy’s team operates. Mr. Ramaswamy is also in Washington for Mr. Trump’s inauguration.

Mr. Ramaswamy had enthusiastically merged his brand with that of the project. He changed his biography on Mr. Musk’s social media platform, X, to “small-government crusader” and shared a picture of himself at the beach reading Congressional Budget Office reports on options for reducing the deficit.

In November, Mr. Trump initially said that the “Great Elon Musk” would work alongside “American Patriot Vivek Ramaswamy” on the project. “Together, these two wonderful Americans will pave the way for my Administration to dismantle Government Bureaucracy, slash excess regulations, cut wasteful expenditures, and restructure Federal Agencies,” he said at the time.

On Monday morning, Mr. Ramaswamy posted a message on X that said “a new dawn,” along with a photo of him and Mr. Musk.

The Biden administration’s goal was for half of all new cars sold by the early 2030s to be electric, meaning that half would still run on fossil fuels.

Existing clean air and fuel economy standards arguably forced automakers to sell more electric cars to comply, but it was up to the automakers to determine what technology to use, and they had until the end of the decade to do so.

General Motors, Hyundai, Volkswagen and other automakers have invested hundreds of billions of dollars to set up assembly lines for electric vehicles and produce batteries domestically. Regardless of what governments do, they have a strong interest in continuing to sell electric cars.

Electric vehicles are also popular with buyers while sales of cars that run on fossil fuels are fading. Hybrid-electric and fully electric vehicles gained 4 percentage points of market share in the United States during the third quarter compared to a year earlier, according to a report this month by the Alliance for Automotive Innovation, which represents most major automakers. The gains came at the expense of gasoline and diesel vehicles.

California and some other states have also required that all cars sold by 2035 be electric. But even that rule allows plug-in hybrids to qualify if they are capable of traveling 50 miles on battery power alone.

The incoming administration is expected to join lawsuits challenging California’s right to set its own standards for motor vehicles.

The portrait of the now retired General Milley went up last week in the last days of the Biden administration. Less than two hours after Mr. Trump took the oath of office, Pentagon officials had taken it down. A U.S. official said that “the White House” ordered the removal. The official declined to speak further.

Mr. Trump has called General Milley “a woke train wreck.” The president has complained in particular about the general’s calls to his Chinese counterpart during the waning weeks of Mr. Trump’s first term, an act the president, in a post on Truth Social, called “so egregious that, in times gone by, the punishment would have been DEATH!”

President Joseph R. Biden Jr. issued a pre-emptive pardon for General Milley before he left office.

Taking down the general’s portrait is unprecedented; the position of chairman of the Joint Chiefs of Staff is viewed as apolitical.

“I hope so,” Mr. Schmerber replied to the television, with some skepticism.

There were immediate changes — especially for migrants with pending appointments to meet with immigration officials — but along much of the border, already quieted by recent Biden administration policy changes, the dominant feeling was anxious anticipation, tinged with confusion.

When Mr. Trump said from the U.S. Capitol that he would send federal troops to the border, Sheriff Schmerber wondered how they would operate legally.

“The soldiers cannot go on private property unless they have permission of the owners,” he said.

And the new president’s portrayal of a nation on its knees might have seemed out of place in Eagle Pass, Texas, which had been ground zero for Gov. Greg Abbott’s clashes with the Biden administration. National Guard troops stood watch in a cold wind in a park, but all was quiet. There had been no illegal crossings from Mexico, or much of anything in recent days.

“It’s pretty dead,” said Spc. Blaine Roldan. Nearby, a tan stray dog the soldiers nicknamed “Pooper” slowly wagged his tail for food not far from a wall of shipping containers and concertina wire installed at Mr. Abbott’s direction.

Hope turned to disappointment for many migrants as they found that their long-sought appointments to meet with federal immigration officials had been suddenly canceled under Mr. Trump’s new administration.

Standing on American soil, steps from the international bridge connecting McAllen, Texas, with Hidalgo, Mexico, Martin Gomez, 45, said he felt defeated by the closure of an app, called CBP One, for migrants seeking to claim asylum and worried that his appointment, scheduled for Aug. 28 in Orlando, Fla., would not happen and that he would have to return to Colombia.

“I think people are going to start crossing illegally,” he said. “At least with CBP One, the government knew where people were going.”

In McAllen, a city with a large population of families with documented and undocumented immigrants, U.S. citizens and migrants with more tenuous holds on the United States, more than a hundred residents gathered to protest Mr. Trump’s incoming administration.

“He’s always portrayed the border as a negative place and immigrants as criminals. I’m here to say that’s not true,” said Karla America Hernandez, 18. “I refer to Martin Luther King. Let’s live in peace.”

In El Paso, Humvees from the Texas National Guard and Texas state police trucks were stationed along the international border Monday, parked and facing the Mexican city of Juarez. Officials said the area had been quiet so far on this Inauguration Day, but that they had orders to keep people away from the river.

“I thought there would be more undocumented people around the bridges, but there was not many,” said Andres Hernandez, 60, a U.S. citizen, as he walked back into El Paso just minutes after Mr. Trump was sworn in.

“It’s very peaceful. We even thought that they would be closing the bridges, but that has not happened,” Mr. Hernandez said.

Mr. Trump also said he planned to declare a national energy emergency. He would be the first president to do so, despite the fact that the United States is currently producing more oil and natural gas than any other country. That declaration could unlock authority to suspend some environmental regulations and speed permits for oil and gas drilling, as well as authority to keep coal-fired power plants running.

“We will drill, baby, drill,” Mr. Trump said in the Capitol after taking the oath of office.

Mr. Trump’s pivot to fossil fuels comes after the hottest year in recorded history and as scientists say the world is running out of time to keep global warming at relatively low levels. Last year, emissions from burning coal, oil and gas helped push average global temperatures past 1.5 degrees Celsius, or 2.7 degrees Fahrenheit, above preindustrial levels. Scientists have said that every fraction of a degree of warming above that level brings greater risks from deadly heat waves, wildfires, drought, storms and species extinction.

Most of Mr. Trump’s energy policies can’t be achieved with the mere stroke of a pen because some would require action by federal agencies or Congress and others could face legal challenges. He also could not, by fiat, rename the Gulf of Mexico to the Gulf of America, or Denali in Alaska, the highest mountain peak in North America, to Mount McKinley. Mr. Trump promised to do both.

But taken together, the declarations underscore how Mr. Trump views the world: America has been weakened by efforts to fight climate change, oil and gas are symbols of strength and power, and plentiful fossil fuels will ensure that the U.S. is able to dominate allies and rivals alike.

The United States is home to “the largest amount of oil and gas of any country on earth, and we are going to use it,” Mr. Trump said during his inaugural address. “We will bring prices down, fill our strategic reserve up again, right to the top, and export American energy all over the world.”

The remarks earned a standing ovation in the Capitol Rotunda, where Mr. Trump spoke, and applause at the Hay-Adams hotel in downtown Washington, where some of the country’s leading oil and gas executives popped champagne and ate mini Pop-Tart pastries with Mr. Trump’s image. The party was sponsored by Harold Hamm, the billionaire founder of Continental Resources, an oil company, who helped raise millions of dollars for Mr. Trump’s campaign.

Mr. Trump’s agenda was a reverse image of his predecessor’s approach. Former President Joseph R. Biden Jr. called climate change an existential threat and said the United States, the world’s largest historic emitter of greenhouse gases, had an obligation to lead the world in curbing fossil fuel pollution.

Mr. Biden never sought an immediate end of coal, oil or gas. But he imposed regulations making it more expensive to operate coal plants, limited future drilling leases and signed laws that invested hundreds of billions of dollars in wind, solar, electric vehicles and other low-carbon technologies in order to lay the groundwork for a transition away from fossil fuels.

“We really moved the clean energy transition forward in a really huge way,” Deb Haaland, Mr. Biden’s interior secretary, said. Mr. Biden “really understood that he had a responsibility to do what he could for the climate crisis,” she said.

Mr. Trump’s efforts to reshape America’s energy landscape could bump up against market realities. U.S. oil production reached new heights last year, and natural gas prices fell to their lowest annual average on record, adjusted for inflation, according to the Energy Information Administration. While many oil and gas companies have asked for looser regulations, they have also said they are not looking to drastically increase output, as doing so most likely would weigh on prices, squeezing profits. By midafternoon on Monday, U.S. oil prices had fallen more than 1 percent as details about Mr. Trump’s energy plans emerged.

“If there’s more energy production, you could see a decline in price from that,” said Jacques White, a petroleum engineer from Colorado, at Mr. Hamm’s party.

During his first term, Mr. Trump’s cabinet secretaries rushed through repeals of environmental regulations, leading many of those efforts to be overturned in the courts.

Some experts also questioned whether Mr. Trump’s declaration of a national energy emergency would be more symbolic than substantive.

“It’s not clear what the emergency is,” said Michael Gerrard, director of the Sabin Center for Climate Change Law at Columbia University. “The U.S. is producing more oil and gas than ever before, more than any other country in the world, we have no gas lines, we have no widespread electricity blackouts.” He called the emergency order “mostly performative.”

In a call with reporters, a White House official said that the emergency declaration was motivated by the idea that U.S. energy costs were currently higher than they should be because of policy decisions by the Biden administration. Interest in artificial intelligence and a boom in data center construction have created an urgent need for more energy, the official said.

Legal experts have identified roughly 150 emergency powers that a president could invoke under certain conditions, such as suspending certain air pollution requirements or ordering the release of certain raw materials from strategic stockpiles. But many of the powers are relatively limited. In his first term, Mr. Trump proposed invoking certain emergency powers to keep unprofitable coal and nuclear plants from retiring, but that effort was eventually abandoned.

Some climate activists had pushed Mr. Biden to declare a national emergency around climate change, but legal experts concluded that doing so “wouldn’t really unlock major powers,” said Daniel Farber, a law professor at the University of California, Berkeley.

On the campaign trail, Mr. Trump promised to unleash oil and gas production and eliminate the “Green New Deal,” his catchall phrase to mean Mr. Biden’s climate policies. Doing so, he promised, would cut grocery and energy prices in half within 18 months of his inauguration.

Environmental groups as well as a coalition of mayors and governors said on Monday that many states, cities and businesses would continue cutting planet-warming emissions on their own.

“The clean energy boom is unstoppable,” said Manish Bapna, president of the Natural Resources Defense Council. “Trump can slow down the transition but he cannot stop it.”

Mr. Trump is expected to order federal agencies to claw back any unspent funds in the Inflation Reduction Act, a sweeping climate and clean energy bill that Mr. Biden signed into law in 2022.

In recent months, however, Biden administration officials have raced to finalize contracts for more than $96.7 billion, or 84 percent of the law’s grants for clean energy, meaning the money can’t easily be pulled back. That includes $8.8 billion for state programs to help consumers buy energy-efficient appliances, $3 billion for cutting air pollution at U.S. ports and $9 billion to help rural electric providers switch from burning coal and gas to alternatives like wind, solar and nuclear power.

That still leaves roughly $11 billion in grants and other spending that has not been finalized, including money for agricultural conservation and a program aimed at helping to reduce pollution in disadvantaged communities.

At the same time, the vast majority of spending in the Inflation Reduction Act, potentially hundreds of billions of dollars, flows through tax credits that companies can claim if they use or manufacture carbon capture technology or various low-carbon energy sources, including wind, solar, batteries, hydrogen, nuclear and geothermal.

Repealing those credits would require Congress to act, and some Republicans whose districts have benefited from the spending have said that at least some of the tax breaks should remain in place.

Mr. Trump, a longtime critic of wind power, also pledged to end federal leasing for large wind farms in federal waters.

The Biden administration has already approved 11 commercial-scale wind farms in the Atlantic Ocean. Some are currently under construction but others have been halted or faced delays because of inflation or supply-chain problems. Several Eastern states — including Massachusetts, New Jersey and New York — have set ambitious renewable energy targets and were hoping to build many more offshore wind farms this decade. Additional projects, however, would require federal approval.

A chuckling Mrs. Clinton, who lost to Mr. Trump in the 2016 presidential election, looked down as she caught the giggles while seated a few feet behind Mr. Trump in the Capitol Rotunda.

Aides indicated that Mr. Trump was serious. A spokeswoman for the president, Karoline Leavitt, said on social media that efforts to rename the Gulf of Mexico would be part of a flurry of Day 1 executive actions.

The shores of the gulf, a 600,000-square-mile, semi-enclosed basin, are shared by Mexico and the United States. Six Mexican states and five American states border the gulf.

The U.S. Board on Geographic Names, part of the U.S. Geological Survey, is responsible for maintaining official geographic names in the United States. It says on its website that it “discourages name changes unless there is a compelling reason.”

The most important considerations for name changes are typically “local use and acceptance,” the website says.

The U.S. Geological Survey did not immediately reply to requests for comment on Mr. Trump’s speech on Monday. The chair of the Board on Geographic Names, Michael Tischler, declined to comment.

Mr. Trump has spoken openly about his desires for American expansion, refusing to rule out using military force to reclaim the Panama Canal or take control of Greenland when speaking at a news conference at his Mar-a-Lago residence in Palm Beach, Fla., this month. It was at that same news conference that he first floated a change in name to the Gulf of Mexico, musing that the phrase “Gulf of America” had “a beautiful ring.”

Even if the U.S. Geological Survey were to change the Gulf of Mexico’s official name in the United States, it is unclear if atlases or other governments would accept the change.

President Claudia Sheinbaum of Mexico has rejected Mr. Trump’s proposal, responding by jokingly suggesting that the United States be called Mexican America.

“It sounds pretty, no?” Ms. Sheinbaum said at a news conference two weeks ago.

The gulf gained its name more than a century before the founding of the United States. As early as the 16th century, the gulf’s name appeared on maps used by Spanish explorers.

Mr. Trump also said on Monday that he intended to rename Denali, which is in Alaska and is the tallest mountain in North America.

In 2015, President Barack Obama used executive powers to change the mountain’s name from Mount McKinley to Denali, an Alaska Native name.

The mountain had officially been called Mount McKinley for almost a century before Mr. Obama’s action.

“We will restore the name of a great president, William McKinley, to Mount McKinley, where it should be and where it belongs,” Mr. Trump said in his inaugural address, referring to the 25th president.

The Senate Armed Services Committee voted Monday to advance the nomination of Pete Hegseth, President Trump’s choice for the position, but the full Senate may not vote on the nomination until later in the week. The vote is expected to be close.

Typically in a transition, a senior politically appointed official from the outgoing administration would stay on as acting secretary until the Senate confirmed the new secretary. Robert O. Work, the deputy defense secretary at the end of the Obama administration, briefly served as acting secretary until Jim Mattis was confirmed as Mr. Trump’s first defense secretary.

Defense Secretary Lloyd J. Austin III resigned effective upon Mr. Trump’s swearing in, as is typical. But no Biden political appointees agreed to fill in, even temporarily, the Defense Department officials said.

Mr. Salesses, a retired Marine Corps officer, is the deputy director of the Pentagon’s Washington-area headquarters services, which is focused on human resources, facilities and resource management.

According to his official Pentagon biography, Mr. Salesses manages annual resources of nearly $1.2 billion, and oversees nearly 4,000 civilian, military, and contractor personnel who provide a full range of financial, contracting, and security services.

Mr. Salesses, who on Monday received a classified intelligence briefing on threats and military missions typical of what’s presented to the secretary each day, previously served as the deputy assistant secretary of defense of continuity and mission assurance, where he oversaw some of the Pentagon’s most sensitive functions, including ensuring that the secretary and deputy secretary had the necessary means to receive and act on top-secret military orders.

Mr. Salesses has also served in top Defense Department policy jobs overseeing the Pentagon’s support for homeland defense missions and domestic crisis management. The uniformed leadership of the U.S. military, including Gen. C.Q. Brown Jr., the chairman of the Joint Chiefs of Staff and the president’s top military adviser, remains unchanged as the Biden administration hands off to the incoming Trump administration.

Helene Cooper contributed reporting.

The move, one of several energy-related announcements in the hours immediately following his inauguration, is yet another about-face in United States participation in global climate negotiations. During his first term Mr. Trump withdrew from the Paris accord, but then President Biden quickly rejoined in 2020 after winning the White House.

Scientists, activists and Democratic officials assailed the move as one that would deepen the climate crisis and backfire on American workers. Coupled with Mr. Trump’s other energy measures on Monday, withdrawal from the pact signals his administration’s determination to double down on fossil-fuel extraction and production, and to move away from clean-energy technologies like electric vehicles and power-generating wind turbines.

“If they want to be tough on China, don’t punish U.S. automakers and hard-working Americans by handing our clean-car keys to the Chinese,” said Gina McCarthy, former White House climate adviser and former head of the Environmental Protection Administration. “The United States must continue to show leadership on the international stage if we want to have any say in how trillions of dollars in financial investments, policies and decisions are made.”

To pull the United States out of the Paris Agreement, the Trump administration will need to formally submit a withdrawal letter to the United Nations, which administers the pact. The withdrawal would become official one year after the submission. It was not immediately clear whether the administration had already submitted the formal withdrawal letter.

U.S. efforts to reduce greenhouse gas emissions were already stalling in 2024, and Mr. Trump’s entry into office makes it increasingly unlikely the United States will live up to its ambitious pledges to cut them even further. Emissions dropped just a fraction last year, 0.2 percent, compared with the year earlier, according to estimates published this month by the Rhodium Group, a research firm.

Despite continued rapid growth in solar and wind power that was spurred by the previous administration’s signature climate legislation, the Inflation Reduction Act, emissions levels stayed relatively flat last year because demand for electricity surged nationwide, which led to a spike in the amount of natural gas burned by power plants.

The fact that emissions didn’t decline much means the United States is even further off-track from hitting Mr. Biden’s goal, announced last month under the auspices of the Paris Agreement, of slashing greenhouse gases 61 percent below 2005 levels by 2030. Scientists say all major economies would have to cut their emissions deeply this decade to keep global warming at relatively low levels.

In a scenario where Mr. Trump rolled back most of Mr. Biden’s climate policies, U.S. emissions might fall only 24 to 40 percent below 2005 levels by 2030, the Rhodium Group found.

“President Trump is choosing to begin his term pandering to the fossil fuel industry and its allies,” the Union of Concerned Scientists said in a statement. “His disgraceful and destructive decision is an ominous harbinger of what people in the United States should expect from him and his anti-science cabinet.”

Since 2005, United States emissions have fallen roughly 20 percent, a significant drop at a time when the economy has also expanded. But to meet its climate goals, U.S. emissions would need to decline nearly 10 times as fast each year as they’ve fallen over the past decade.

The United States is also a major exporter of emissions. Because of policies promoted by both Republicans and Democrats, the United States is now producing more crude oil and natural gas than any nation in history. Mr. Trump has vowed to further ramp up production and exports.

While the United States may not be party to the Paris Agreement, it will still be part of the U.N. Framework Convention on Climate Change, which hosts annual climate negotiations known as COPs. This year’s COP will be held in Brazil in November and nations will be announcing new pledges for emissions reductions.

One recent study by Climate Action Tracker, a research group, found that, if every country followed through on the pledges they have formally submitted so far, global average temperatures would be on track to rise roughly 2.6 degrees Celsius, or 4.7 degrees Fahrenheit, above preindustrial levels by the end of the century, well above the 1.5 degrees Celsius the Paris Agreement originally set as a goal.

“Trump’s irresponsibility is no surprise,” said Christiana Figueres, a Costa Rican diplomat and an architect of the Paris Agreement in 2015. “In time, Trump will not be around but history will point to him and his fossil fuel friends with no pardon.”

“I am in shock,” said Maura Hernandez who received the news this morning as she arrived in Tijuana with her four small children from the state of Michoacán, one of Mexico’s most violent states. She had a scheduled appointment on Tuesday.

“I don’t know what is going to happen to us,” she said, adding that they had fled their homes amid rampant insecurity. “I had a whole plan and now life has made a horrible turn.”

Gustavo Selva from Venezuela had received the hopeful news of his scheduled appointment 21 days ago. Over the weekend, however, he received an email informing him it had been delayed until Feb. 9.

“We are so disappointed,” he said after reading the update on his phone.

By then he had already traveled to Tijuana from the southern state of Chiapas, where he had waited for seven months for his appointment to go through.

“We thought we could enter today without a problem; now we will be stranded here indefinitely,” Mr. Selva added.

Uncertainty and confusion reigned in this popular border crossing as more and more migrants read or heard the news, while many stayed in line saying they would wait until an immigration officer told them otherwise.

“This is so hard,” said Juan Antonio Nieto, who left El Salvador four months ago and had a scheduled appointment for Monday. “If the government does not let us in, we don’t know what we are going to do, we have no money to go back.

“But until someone tell us we can’t go in, we still have faith in God they will allow us in,” Mr. Nieto added.

A Mexican immigration officer said that as of 9:30 a.m. Monday morning, there had been “no logistical changes” to deal with migrants who had a scheduled appointment for today.”

Aline Corpus contributed reporting.

That setup violates the law, the nonprofits said in their lawsuits.

The 1972 Federal Advisory Committee Act says that committees of outside government advisers must be “fairly balanced in terms of the points of view represented,” and that they must make their records available to the public.

The lawsuits say that Mr. Musk and Mr. Ramaswamy’s effort meets neither of those requirements. They say its leaders all share one viewpoint: that the size and cost of government should be cut drastically.

All the suits asked federal judges to stop the cost-cutting effort until it complies with the law.

One of Monday’s lawsuits was filed by a coalition that includes the American Federation of Government Employees, a union of federal workers, as well as a watchdog group called State Democracy Defenders Fund. In the other case, the plaintiffs include the liberal good-government group Citizens for Responsibility and Ethics in Washington and the American Federation of Teachers.

“The question every American should be asking is ‘What are they hiding?’” said Skye Perryman, the chief executive of a legal nonprofit called Democracy Forward, which is representing the second group of plaintiffs. “DOGE must not be allowed to operate in the shadows.”

The third suit was filed by a nonprofit called National Security Counselors, which represents federal whistle-blowers.

Katie Miller, a spokeswoman for the operation, did not immediately respond to questions.

The program, which debuted in early 2023, allowed 1,450 migrants a day to schedule a time to present themselves at a port of entry and seek asylum through U.S. immigration courts. More than 900,000 migrants entered the country using the app from its launch in the beginning of 2023 to the end of 2024.

A former Department of Homeland Security official who spoke on the condition of anonymity said that around 30,000 migrants had appointments to enter the United States through the app as of Monday morning.

At the El Chaparral border crossing in Tijuana, Mexico, dozens of migrants who stared at their phone screens trying to check whether their appointments were still valid instead found the crushing message that they no longer existed.

“I am in shock,” said Maura Hernandez, who received the news on Monday morning as she arrived in Tijuana with her four small children from the state of Michoacán. She had a scheduled appointment on Tuesday.

“I don’t know what is going to happen to us,” she said, adding that they had fled their home amid rampant insecurity.

The program was a key part of the Biden administration’s effort to gain control over migration through the southern border. On the one hand, the administration blocked asylum for migrants who crossed illegally. At the same time, U.S. officials believed that by offering migrants an organized way to enter legally through an app, they could discourage attempts to gain entry without authorization. Border numbers have dropped dramatically in recent months, and officials believe the program is a major reason.

“I would say that the model that we have built of restricting asylum at our southern border and building accessible, lawful, safe and orderly pathways for individuals to seek relief under our laws is the model that should be sustained,” said Department of Homeland Security Secretary Alejandro Mayorkas in an interview with NPR this month. “And we have delivered the border and those accessible pathways to the incoming administration.”

The end of the program will test that theory as the Trump administration moves toward a more restrictive policy at the border. The former homeland security official said that they estimated that, in total, nearly 300,000 migrants were in Mexico waiting to use the app.

“We are so disappointed,” said Gustavo Selva from Venezuela after reading the update on his phone that the program had been shut down. He had received hopeful news of his scheduled appointment 21 days ago.

Two days ago, however, he received an email informing him that it had been delayed until Feb. 9. By then, he had already traveled to Tijuana from the southern state of Chiapas after waiting there for seven months for his appointment to go through.

“We thought we could enter today without a problem,” Mr. Selva added. “Now we will be stranded here indefinitely.”

Critics of the program, especially Republican lawmakers, viewed it as a way to allow those who otherwise had no way of entering the U.S. to come into the country and remain for years as their immigration cases languished in the courts.

“The fact that this application exists is the most underreported scandal of the Biden admin. They made an application to facilitate illegal immigration. It boggles the mind,” Vice President JD Vance said in a social media post last week.

Matthew Hudak, a former senior Border Patrol official, said the decision was a clear sign that things were changing at the southern border.

“Simply wanting to immigrate to the U.S. and signing up to get in line will be replaced by more stringent policies that will significantly raise the bar for those seeking to come here, including reimplementing the Remain in Mexico program,” he said. “Many will be left to decide if they will work through the legal process or attempt to enter the country illegally and face what will likely be much more significant consequences.”

Aline Corpus contributed reporting from Tijuana, Mexico.

The New York Times compared estimates from several research organizations and the federal government, as well as more recent administrative data, to better understand this population, and who might be most vulnerable to Mr. Trump’s immigration crackdown.

Who Are the Millions of Immigrants Trump Wants to Deport?

Trump wants to end several programs that offered new arrivals temporary relief. Millions of others without legal status may also be vulnerable to deportation.

The topics Mr. Trump will direct his officials to investigate in an executive order Monday will be extensive, including trade deficits and trade deals signed with China, Canada and Mexico. That could tee up the ability of the president to deploy tariffs on numerous targets for many different reasons, potentially scrambling international supply chains and spawning global trade wars in the weeks and months to come.

The executive order will direct federal agencies to examine unfair trade and currency practices and to assess whether foreign governments have complied with terms of the two trade deals Mr. Trump signed in his first presidency. It will also require the government to assess the feasibility of creating an “External Revenue Service” to collect tariffs and duties

Mr. Trump is also ordering a study of tariffs that the United States has imposed for national security reasons, as well as the use of a special trade exemption, called de minimis, that allows low-value goods to come into the United States tariff free. That loophole has allowed large volumes of Chinese goods to escape the tariffs Mr. Trump slapped on China during his first term. The details of the executive order were earlier reported by The Wall Street Journal.

While Mr. Trump has decided to hold off on tariffs for now, his advisers say he remains more convinced than ever that they can be used to great advantage.

The president and his advisers have been favoring a combination of policies, including a universal tariff on foreign products, a higher tariff on China and separate measures that could address the trade relationship with Mexico and Canada by imposing taxes on those countries as well, people familiar with the plans said.

In his inauguration address on Monday, Mr. Trump said he would “immediately begin the overhaul of our trade system to protect American workers and families.”

There will be “massive amounts of money pouring into our Treasury” because of tariffs, he said. “The American dream will soon be back and thriving like never before.”

Mr. Trump has praised tariffs for their ability to help U.S. factories, raise revenue to help pay for the tax cuts he hopes to enact and generally serve as a source of leverage in negotiations with foreign countries.

While managing trade is technically the domain of Congress, various trade laws have given the president wide-ranging powers to issue tariffs. The president can use them to defend U.S. national security, answer back to unfair trade practices and counter various types of international emergencies.

Mr. Trump and his advisers are continuing to debate the best method to use to issue their tariffs, but they believe they have the legal authority to use any of them, people familiar with the deliberations said.

Some U.S. manufacturers credit the tariffs that Mr. Trump imposed during his first term — and that President Joseph R. Biden Jr. kept in place — with helping their businesses survive amid intense competition from countries like China. But economists and many other businesses argue that tariffs can cause economic harm, as they raise the prices of imported goods and incite retaliation from other governments that can hurt U.S. exports.

Mr. Trump’s executive order will keep foreign governments on notice in the coming weeks, as they try to establish closer ties with his administration and convince the president not to target them.

Canadian officials have drawn up a list of American goods they intend to tax in return if hit by Mr. Trump’s tariffs, including Florida orange juice, Tennessee whiskey and Kentucky peanut butter. Mexico has also threatened retaliatory tariffs on American exports, as has the European Union and other governments.

During his first term, Mr. Trump rocked the country’s global trade relationships by imposing tariffs against foreign washing machines, solar panels, metals and a variety of products from China. Those moves nearly doubled the average tariff rate applied to imported goods, though U.S. tariffs still remained comparatively low by international standards.

Economists have expressed concerns about Mr. Trump’s plans to expand those taxes. They say that, while tariffs can help certain protected American industries, they have other downsides for the economy, including raising costs for households and businesses that rely on imported products.

Lydia Cox, an economist at the University of Wisconsin-Madison, described tariffs as “a pretty blunt instrument” in an online forum hosted by the Harvard Kennedy School last week.

There are some potential benefits for protected industries from tariffs, she said, “but they create a lot of collateral damage along the way.”