Defense Secretary Pete Hegseth, who disclosed the war plans in the chat this month, condemned Mrs. Clinton’s actions during a Fox News segment in November 2016.

“Any security professional — military, government or otherwise — would be fired on the spot for this type of conduct and criminally prosecuted for being so reckless with this kind of information,” he said.

Mr. Hegseth was also adamant that anyone engaging in similar acts should be summarily punished.

“People have gone to jail for one one-hundredth of what, even one one-thousandth of what Hillary Clinton did,” he said during a Fox Business segment that same month.

Secretary of State Marco Rubio, another participant in the encrypted group chat, also voiced those sentiments in a Fox News appearance in 2016, when he was running for president.

“People are going to be held accountable if they broke the laws of this country,” he said. He added that “nobody is above the law, not even Hillary Clinton.”

Several Defense Department officials said on Monday that by putting U.S. war plans into a commercial chat app, Mr. Hegseth risked compromising national security — and had potentially violated the Espionage Act, a law that governs how national security information is handled.

But members of the group chat still pointed to Mrs. Clinton’s use of the private email server years later as they denounced the Justice Department for indicting President Trump in 2023 over his handling of classified documents.

“How is it Hillary Clinton can delete 33,000 government emails on a private server yet President Trump gets indicted for having documents he could declassify?” Michael Waltz wrote on his Twitter account in 2023, when he was a representative from Florida.

Mr. Waltz had reached out to Jeffrey Goldberg, the editor in chief of The Atlantic, shortly before Mr. Goldberg was added to the group of officials discussing the planned strikes on Yemen this month, Mr. Goldberg wrote in an article published on Monday.

Karoline Leavitt, the White House press secretary, said on social media on Tuesday that the war plans Mr. Hegseth shared in the chat were not classified. But using a commercial app to plan and coordinate military operations would be a violation of rules dictating that sensitive operations should be discussed only on secure lines and officially approved platforms to reduce the risk of adversaries spying on communications that could compromise national security.

Stephen Miller, the White House deputy chief of staff and Mr. Trump’s homeland security adviser, told the group chat that the president had given a “green light” for the strike against the Houthis in Yemen, according to Mr. Goldberg. But in 2022, Mr. Miller had shared his thoughts on the dangers of using improperly secured platforms to conduct official business.

“One point that doesn’t get made enough about Hillary’s unsecured server illegally used to conduct state business (obviously created to hide the Clintons’ corrupt pay-for-play): foreign adversaries could easily hack classified ops & intel in real time from other side of the globe,” Mr. Miller wrote on social media.

The officials who participated in the Signal chat have tried to downplay their actions since the Atlantic article was published. Mr. Hegseth told reporters on Monday that “nobody was texting war plans,” even though he was the official who shared the detailed plan to strike Yemen, according to The Atlantic.

When Mr. Trump was asked about the Atlantic article on Monday, he said, “I don’t know anything about it.” The president was not reported to be in the Signal group.

And Mrs. Clinton weighed in on social media on Monday with a screenshot of the top of the Atlantic article and an emoji of a pair of eyes. “You have got to be kidding me,” she wrote.

“1. No “war plans” were discussed. 2. No classified material was sent to the thread,” Ms. Leavitt said in a post on social media as she attacked Mr. Goldberg. Several Defense Department officials have expressed shock over the inclusion of such sensitive information in a chat group on a commercial app.

The article in The Atlantic said the chat included “operational details of forthcoming strikes on Yemen, including information about targets, weapons the U.S. would be deploying, and attack sequencing.”

The extraordinary breach of American national security intelligence has led Democrats to call for the resignation of the national security adviser, Michael Waltz, who set up the group chat, and the defense secretary, Pete Hegseth, who reportedly shared classified war plans in it.

It has also frustrated some Republicans. Representative Don Bacon, Republican of Nebraska and a senior member of the Armed Services Committee, told reporters that the White House should “be honest and own up” to putting classified information on an unclassified system.

“It’s a fact,” Mr. Bacon said. “Classified information was put out by the secretary of defense. It’s pretty clear,” he said.

In an article published on Monday, Mr. Goldberg wrote that he was mistakenly added to the group on Signal by Michael Waltz, the national security adviser. The group also included Vice President JD Vance and Secretary of State Marco Rubio.

Mr. Goldberg wrote that on Saturday, two hours before U.S. strikes on Houthis in Yemen, Mr. Hegseth posted operational details in the chat. Mr. Goldberg did not directly quote or post a screenshot of that update because it “could conceivably have been used to harm American military and intelligence personnel,” he wrote. He did post screenshots of other parts of the conversation with the senior officials.

On Monday, the National Security Council appeared to confirm the authenticity of the chat.

“At this time, the message thread that was reported appears to be authentic, and we are reviewing how an inadvertent number was added to the chain,” said Brian Hughes, the National Security Council spokesman.

After the report was published on Monday, Mr. Hegseth denied war plans were shared in the group chat, prompting Mr. Goldberg to tell CNN that Mr. Hegseth was lying.

Here’s the latest.

What has the White House said?

President Trump told NBC News on Tuesday that the leak was “the only glitch in two months, and it turned out not to be a serious one.”

Karoline Leavitt, the White House press secretary, posted on social media that “no ‘war plans’ were discussed” and “no classified material was sent to the thread.” That contradicts Mr. Goldberg, who wrote that he had not published some of the messages in the thread because he said they contained sensitive information.

Mr. Goldberg’s report also raised concerns about administration officials using Signal, a nonsecure messaging platform, and setting the messages to automatically delete. Ms. Leavitt pushed back against those concerns.

“The White House Counsel’s Office has provided guidance on a number of different platforms for President Trump’s top officials to communicate as safely and efficiently as possible,” she wrote.

After the Atlantic report, Brian Hughes, a spokesman for the National Security Council, said in a statement on Monday that the message thread “appears to be authentic.” Mr. Hughes said officials were “reviewing how an inadvertent number was added to the chain.”

The administration has tried to discredit Jeffrey Goldberg.

When Mr. Trump was first asked Monday about the report, he said he was not aware of the leak, but he immediately attacked the magazine.

“I’m not a big fan of The Atlantic,” he said. “To me, it’s a magazine that’s going out of business.”

For years, Mr. Trump has complained about Mr. Goldberg and his publication because of an article the journalist published in 2020 that said that Mr. Trump had declined to visit a cemetery of fallen American soldiers in France because it was “filled with losers.”

Mr. Hegseth similarly criticized Mr. Goldberg on Monday, calling him a “deceitful and highly discredited so-called journalist” after landing in Hawaii, his first stop before a weeklong trip to Asia.

“Nobody was texting war plans, and that’s all I have to say about that,” Mr. Hegseth said.

Mr. Goldberg said “that’s a lie” on CNN in response to Mr. Hegseth’s comments.

Will Mr. Waltz face consequences?

Mr. Trump said Tuesday that Mr. Waltz would not face consequences after Mr. Goldberg wrote that the national security adviser had added him to the Signal chat.

“Michael Waltz has learned a lesson, and he’s a good man,” Mr. Trump told NBC News. The president said one of Mr. Waltz’s staff members had added Mr. Goldberg.

But even before Monday’s leak, Mr. Waltz faced skepticism from inside and outside of the administration. Some of Mr. Trump’s most conservative allies viewed him as not loyal enough to the president while some of the Republicans he formerly served with in Congress considered him too loyal.

What did Vice President JD Vance say in the chat?

In the Signal chat, Mr. Vance raised concerns about the Yemen attack, writing that he thought the administration was “making a mistake.” Mr. Vance said he worried Americans would not “understand this or why it’s necessary” to launch the attacks. He noted that only 3 percent of U.S. trade runs through the Suez Canal, a shipping route threatened by the Houthis, compared with 40 percent of European trade.

“I am willing to support the consensus of the team and keep these concerns to myself,” Mr. Vance wrote. He later wrote, “I just hate bailing Europe out again.”

Mr. Vance’s comments revealed some disagreement within the senior ranks of the administration, a remarkable development especially from Mr. Vance, who has gone to great lengths to present a unified front with the president. A spokesman for Mr. Vance denied any dissent from the vice president.

“The vice president’s first priority is always making sure that the president’s advisers are adequately briefing him on the substance of their internal deliberations,” the spokesman, William Martin, said in a statement. “Vice President Vance unequivocally supports this administration’s foreign policy. The president and the vice president have had subsequent conversations about this matter and are in complete agreement.”

How are both parties responding?

Democrats are furious about the report, and they are demanding investigations into the disclosure of sensitive material. Some are also calling attention to the Trump administration’s efforts to downplay the incident, resurfacing clips of Mr. Waltz and other Trump allies criticizing Hillary Clinton’s use of a private email server as secretary of state.

Ms. Clinton posted a link to the Atlantic article on social media on Monday with an emoji of two eyes and wrote, “You have got to be kidding me.”

Several Republicans on Capitol Hill expressed concerns about Mr. Goldberg’s inclusion in the chat and acknowledged that it was a mistake. Most, however, said they wanted a full briefing before drawing any conclusions.

Representative Brian Fitzpatrick, a Pennsylvania Republican who sits on the House Intelligence Committee, said on CNN that his panel would send an inquiry to the Office of the Director of National Intelligence and then determine whether a fuller investigation was warranted. But Speaker Mike Johnson, Republican of Louisiana, dismissed the idea of additional investigations or discipline for the officials involved.

Still, some of Mr. Trump’s most loyal allies downplayed the incident. Sean Hannity, the Fox News host, said the story was a “smear” that is being “waged by the left.”

“I just hate bailing out the Europeans again,” wrote Vice President JD Vance, asserting that the strikes would benefit Europe far more than the United States.

“I fully share your loathing of European freeloading,” Pete Hegseth, the secretary of defense, later replied. “It’s PATHETIC.”

The exchange seemed to show real feelings and judgments — that the Europeans are mooching and that any American military action, no matter how clearly in American interests as well, should be somehow paid for by other beneficiaries.

A member of the chat identified as “SM,” and believed to be Stephen Miller, a top aide to President Trump, suggested that both Egypt and “Europe” should compensate the United States for the operation. “If Europe doesn’t remunerate, then what? If the US successfully restores freedom of navigation at great cost there needs to be some further economic gain extracted in return,” SM wrote.

The apparent disregard by administration officials of security protocols by having such a discussion — which included operational details — on a consumer chat app, even an encrypted one, prompted concern that Russia and China could be listening in.

“Putin is now unemployed: No point in spying anymore,” Nathalie Loiseau, a member of the European Parliament, wrote on X, saying the leaks now came from the Americans themselves. “No point in crushing Ukraine anymore, Trump will take care of it.”

The commentary in the exchange is the latest blow to one of the world’s most storied alliances, which took generations to build and strengthen but which the Trump administration has managed to weaken in mere weeks.

“It is clear that the trans-Atlantic relationship, as was, is over, and there is, at best, an indifferent disdain,” said Nathalie Tocci, director of Italy’s Institute of International Affairs, who formerly advised a top E.U. official. “And at worst, and closer to that, there is an active attempt to undermine Europe.”

The European Union is, in many ways, the antithesis of the principles that Mr. Trump and his colleagues are championing. The bloc is built around an embrace of international trade based on rules. It has been at the forefront of climate-related regulation and social media user protections.

Europe has been on alert ever since Mr. Vance delivered a speech at a security conference in Munich last month that questioned European values and its democracy and shocked European leaders. He followed that up by warning that Europe was at risk of “civilizational suicide.”

If the relationship between the United States and Europe were merely transactional, it would be relatively easy for Europeans to just spend more on the military and give Mr. Trump some sort of victory, said François Heisbourg, a French analyst and former defense official.

But in Mr. Vance’s speech attacking European democracy in Munich, let alone in the newly public exchange, the distaste for Europe is about more than transactions.

“Vance was quite clear: We don’t share the same values,” Mr. Heisbourg said.

He and others, like Anna Sauerbrey, the foreign editor of Die Zeit, noted that the explicit demand for payment, rather than just political and military support, as in Iraq and Afghanistan, was new. And it ignored the fact that “the U.S. depends on global trade,” she said, and that “France, Britain and the Netherlands have deployed ships to the region” for the same purpose. The Americans, she said, “are constantly overlooking European efforts.”

China, for example, gets most of its oil imports through the Strait of Hormuz and does much of its export trade with Europe through the same sea route. But no one is asking China to pay, Ms. Tocci noted.

For months, Washington has been sending barbed statements and actions Europe’s way.

Mr. Trump has made it clear that he wants to acquire Greenland, a semiautonomous territory of Denmark, even as European leaders warn that they will defend territorial integrity. Usha Vance, Mr. Vance’s wife, and Mike Waltz, the national security adviser, are visiting the island this week, uninvited, its government says, and to an agitated response.

Mr. Trump has also repeatedly warned that Europe must pay much more for its own defense, threatening not to come to the aid of nations that do not pay up sufficiently, and has pivoted sharply away from Ukraine. He has simultaneously rolled out plans to slap hefty tariffs on Europe and argued that the European Union was created to “screw” America.

Christel Schaldemose, a Danish politician who is a center-left member of the European Parliament, said the way the U.S. has been talking about the E.U. in general lately is “not helping.”

“Could we start talking to each other as allies and not enemies?” she said.

Even as European leaders try to maintain the friendship, they are racing to try to bolster their defense expenditures, cognizant that it would be nearly impossible to replace American military capabilities overnight.

They are meeting on Thursday in Paris to discuss Ukraine, and NATO foreign ministers meet early next month to discuss progress.

They are also scrambling to strike a trade deal with the United States, with the E.U. trade commissioner headed to Washington on Tuesday to talk with his American counterparts.

But with America’s increasingly hostile attitude toward Europe, the continent’s officials are contemplating a future where the prized relationship stretching across the Atlantic, a foundation upon which decades of relative peace and prosperity have been built, might never be the same.

“The international order is undergoing changes of a magnitude not seen since 1945,” Kaja Kallas, the top E.U. diplomat, said last week, echoing a line from the bloc’s defense preparedness plan, which is meant to help Europe to become more militarily independent.

Splintering from the United States is an expensive prospect. The E.U. has already unveiled an initiative that could be worth 800 billion euros, about $865 billion, to help European nations achieve desired military spending levels.

Still, the group chat leak underscores why a divorce may be necessary: The United States is not the reliable ally it once was, either rhetorically or practically.

It is highly unusual and possibly illegal for sensitive military plans to be discussed on a messaging app, rather than by a more secure means of communication.

That disregard for normal security procedures will “cause allies to be very reluctant to share analysis and intelligence,” said Ben Hodges, former commander of U.S. forces in Europe. Barring major change, people “will assume America can’t be trusted.”