A veteran of the Watergate prosecution is now serving in a pivotal role in the Trump-Russia probe. Sources familiar with Bob Mueller’s investigation of Russian efforts to interfere in the 2016 election confirmed to The Daily Beast that James Quarles is the probe’s point person for dealing with the White House.

One source said Mueller himself is always “fully up to date on the White House portion” of the probe, and that Quarles handles the bulk of the day-to-day interactions between the White House and the special counsel. He communicates with the White House several times a week regarding Mueller’s queries, document requests, and planned interviews. As the probe progresses, the White House team’s communication with Quarles has become increasingly frequent.

The Trump-Russia investigation gets compared to Watergate approximately every 15 seconds by a member of Washington’s pundit class. But the talking heads rarely mention that a Watergate veteran is a key player in the case. Before joining the Russia probe, Quarles’ last job in government was on the Watergate prosecution. He focused on campaign finance during his time there, from 1973 to 1975, according to Wired.

“That’s really where he learned how to investigate and explore whether there’s proof for potential legal theories,” said a person who has worked with Quarles.

Richard Ben-Veniste, one of the lead Watergate special prosecutors, told The Daily Beast he found Quarles to be a formidable figure during their time together on the probe.

“Jim Quarles has always impressed me as being very smart and understated, with an encyclopedic knowledge of the law,” Ben-Veniste said.

In 1975, after leaving the probe, Quarles took a position at the firm WilmerHale (then called Hale and Dorr), where he has spent his career. He and Mueller were there when Mueller made a brief foray into private practice after heading the Justice Department’s Criminal Division. Sources said Mueller and Quarles have been friends since their time together there—so, for more than 20 years.

Quarles is one of the probe’s most senior members. He’s also one of just a handful of lawyers to leave private practice for positions on the probe. During his time at WilmerHale, he specialized in complex civil litigation, according to FindLaw.com, including class action suits, intellectual property matters, and issues before the International Trade Commission and the Securities and Exchange Commission.

“He’s one of these wise old men who, given his range of experience, is just a good reality-check on getting things done, and getting them done the right way, particularly with high-profile matters,” said the person who has worked with him. “He’s been around the block, and he is pretty skilled at avoiding potential landmines, whatever they may be.”

Sources who spoke with The Daily Beast described the White House’s relationship with Mueller’s team—and Quarles in particular—in overwhelmingly positive terms: as open, professional, and communicative.

One source said the White House shouldn’t rest easy just because their interactions with Mueller and Quarles have been amicable.

“Just because somebody is open, kind, gracious and professional doesn’t mean that everything is going to work out the way you want it to work out,” said a person familiar with Mueller’s probe.

Meanwhile, sources said Andrew Weissmann—known for his bulldog-style approach to prosecutions—appears to be leading the investigation into Paul Manafort, who ran Trump’s campaign for about three months in the summer of 2016.

A white-collar criminal defense lawyer who has faced Weissmann in court told The Daily Beast he will likely treat Manafort like he’s in a mob investigation.

“He doesn’t—at least he didn’t, back in the day—shy away from saying, ‘You did something wrong and I’m going to prove it,’” the lawyer said of Weissmann.

Already, there’s been tension between Team Mueller and Team Manafort. Not only has his spokesman been subpoenaed, so have the heads of lobbying shops who worked alongside Manafort to boost a Putin ally. The ill will crystallized when the FBI raided Manafort’s house in August—an aggressive move that was viewed as a threat to other people in the scope of Mueller’s probe.

(On Monday night, two sources told the New York Times that Mueller followed the raid by warning Manafort that he would soon be indicted. Meanwhile, CNN reported that Manafort was wiretapped under the Foreign Intelligence Surveillance Act—once before the election, and again after Trump had won the race for the presidency.)

Leslie Caldwell, former head of the Justice Department’s Criminal Division, has worked closely with Weissmann over the years. She said that when he’s running an investigation, he doesn’t waste time.

“Andrew has a real nose for fraud and criminal wrongdoing and corruption, and he’s really skilled at seeing what’s there and getting to it quickly and effectively,” she said. “He doesn’t get bogged down in the kinds of side issues that sometimes weigh down white collar investigations.”

Sources told The Daily Beast that Greg Andres, a veteran trial lawyer, has also done work investigating Manafort as part of the Mueller probe. Andres was a prosecutor in the Eastern District of New York and at the Justice Department’s Washington, D.C. headquarters before joining the firm Davis Polk. During his time in government, one of his specialties was prosecuting companies that bribed foreign officials. He’s also an expert in money-laundering and white-collar crime. And in New York, he prosecuted the mob.

Andres and Quarles are two of a handful of lawyers on Mueller’s team who left private practice gigs—and took major pay cuts—to investigate potential coordination between Team Trump and the Kremlin.

The last time Quarles was in government, more than four decades ago, he spent years investigating a historic case. How long this probe will last is anyone’s guess.