Special counsel Robert Mueller is assembling a prosecution team with decades of experience going after everything from Watergate to the Mafia to Enron as he digs in for a lengthy probe into possible collusion between Russia and President Donald Trump’s 2016 campaign.

His first appointments — tapping longtime law-firm partner James Quarles and Andrew Weissmann, the head of the Justice Department’s criminal fraud unit — were the opening moves in a politically red-hot criminal case that has upended the opening months of the Trump White House.

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Mueller is expected to take an expansive view of his role. He inherited a spate of existing federal probes covering figures including the president’s son-in-law and senior White House adviser, Jared Kushner, and former campaign hands Paul Manafort, Michael Flynn and Carter Page.

Mueller brings a wealth of national security experience from his time leading the FBI in the aftermath of the Sept. 11, 2001, attacks. Veteran prosecutors say he has assembled a potent team whose members have backgrounds handling cases involving politicians, mobsters and others — and who know how to work potential witnesses if it helps them land bigger fish.

“The more familiar you are with the important, hard cases that have come before you, the better you are at assessing the one in front of you,” said Samuel Buell, a former federal prosecutor who worked with Weissmann on the Enron case in the early 2000s.

“In a matter of this importance — it’s going to have an almost unprecedented level of outside scrutiny for anything they do — it’s critical that Mueller would be prizing that kind of gray-beard energy,” Buell said.

Mueller and his new staff have spent their first weeks holding briefings on everything that’s been done over the past year by the FBI, Justice Department and the U.S. attorney’s office in Alexandria, Virginia, on the probes into the 2016 election — work that now falls under their umbrella.

Peter Carr, a spokesman for Mueller, confirmed in an email to POLITICO that the special counsel’s office won’t start from scratch but can “move forward on investigative steps already taken.”

Here’s a rundown of everything we know about Mueller’s probe so far:

Who’s on Mueller’s staff?

Mueller’s prosecution team is full of familiar faces — to him.

He already has picked three former colleagues from his last job as a partner at the Wilmer Cutler Pickering Hale & Dorr law firm: Aaron Zebley, who also was Mueller’s FBI chief of staff; Jeannie Rhee, a former DOJ attorney; and Quarles, who got his start in Washington some four decades ago as an assistant Watergate prosecutor.

But Mueller’s biggest hire to date was Weissmann, who is taking a leave from his current post leading the Justice Department’s criminal fraud section. The two men have a long history together at the FBI, where Weissmann served as both the bureau’s general counsel from 2011 to 2013 and as Mueller’s special counsel in 2005.

Weissmann’s prosecution record includes overseeing the investigations into more than 30 people while running the Enron Task Force, including CEOs Kenneth Lay and Jeffrey Skilling. And while working in the U.S. attorney’s office in the eastern district of New York, he tried more than 25 cases involving members of the Genovese, Colombo and Gambino crime families.

Former Obama DOJ spokeswoman Emily Pierce called Weissmann “an inspired choice” to help Mueller lead the Russia probe.

“As a fraud and foreign bribery expert, he knows how to follow the money. Who knows what they will find, but if there is something to be found, he will find it,” she said.

Mueller has more spaces to fill. Cliff Stricklin, a former assistant U.S. attorney who worked with Weissmann on the Enron case, said the “ideal team for something like this” would be around six to eight prosecutors.

The special counsel will also add administrative assistants and is likely to tap experts from other agencies as specialized needs arise. That could include Treasury Department staffers who know about money laundering or IRS agents who could help untangle complicated tax returns. FBI agents also are likely to cycle through, though that number isn’t likely to be very large.

“I’d not expect a massive army of agents here by any stretch,” Buell said.

Carr, the Mueller spokesman, said the special prosecutor is initially “focused on providing a management structure to oversee ongoing matters” in the Russia probe, and he said the number of staffers who will be appointed to join the probe “will be determined by the needs of the investigation.”

What happens to all the existing federal investigatory work?

Mueller’s team will pick up where other probes left off, including an FBI investigation that started last July exploring possible links between the Trump campaign and Moscow. They’re also taking on the Manafort probe, which The Associated Press reported started in 2014 — before Manafort became Trump’s campaign manager — when federal officials started looking into his work on behalf of pro-Kremlin officials in Ukraine.

Also under Mueller’s purview: The government’s investigation of Flynn, the former White House national security adviser who has come under scrutiny on multiple fronts, including for lobbying on behalf of a Turkish businessman with ties to Russia.

Reuters previously reported that a grand jury in northern Virginia has approved subpoenas to Flynn’s business associates, and veteran prosecutors say that work will now be handed over to the special counsel.

“Obviously, Flynn and Manafort and all the people connected in the campaign are going to be looked at,” said Peter Zeidenberg, a former federal prosecutor who worked at DOJ during the George W. Bush-era Valerie Plame Wilson investigation. “That seems self-evident.”

How wide will the Mueller probe go?

From the get-go, DOJ gave Mueller leverage to take the Russia probe wherever he thinks it needs to go. The original mandate cleared him to explore “any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump,” and it also gave the green light on “any matters that arose or may arise directly from the investigation.”

Former federal prosecutors say Mueller is likely to examine any financial ties between Russia, Trump and his business partners; the hacks into the Democratic National Committee and Hillary Clinton campaign manager John Podesta; and even Trump’s decision last month to fire FBI Director James Comey.

As they dig, Mueller and his team could find useful evidence in Trump’s personal Twitter feed, which Zeidenberg said is a “gold mine” of time-stamped thoughts and opinions from the president on matters under investigation. They’ll also be positioned to study posts from associates like Roger Stone, who openly touted his communications with Russian hackers and associates of WikiLeaks last summer just before the site posted stolen emails from Podesta.

Mueller’s team also will be on the lookout for evidence of obstruction of justice, such as the destruction of any records that could have provided links between the Republican president, his campaign and Russia.

Carr declined to comment on the breadth of the probe, but he said Mueller does not think he’s limited to any particular federal court district jurisdiction, meaning he can bring cases in any federal court in the country. He also does not need approval from DOJ’s national security or criminal divisions to take routine steps in the investigation.

How long will Mueller’s probe last?

Veteran prosecutors say Mueller won’t move as quickly as House and Senate committees that have already demanded materials from key Trump associates, including Manafort, Stone, Page and Flynn.

“You don’t go talk to potential targets first,” Zeidenberg said. “They’re at the end. I don’t think they’re anywhere close to that.”

Mueller’s team has to propose a budget by mid-July, but other than that, there are no deadlines.

Former prosecutors say the investigation could last two years or more before it produces a final report to the Justice Department. In the meantime, they say he can recommend grand jury indictments if his team uncovers illegal activity.

“I’d think he’d be reluctant to reach the reporting stage on this before he felt he’d really run to the ground most of the big stuff,” Buell said. “But he wouldn’t have to wait until he turns out the lights and vacates the office to do that.”