Robert Mueller, the newly named special counsel investigating potential collusion between the Trump campaign and Russian officials, may find himself in the extraordinary position of questioning President Donald Trump.

There is precedent for this. John Danforth, the only other person to be named a special counsel under the same statute as Mueller, told The Daily Beast on Wednesday that he conducted a phone interview with Bill Clinton as part of his investigation into the Waco siege. He said it was the only contact he had with anyone in the White House during the investigation, and he did it “in the name of thoroughness.”

Mueller may need to be similarly thorough.

“That’s investigative procedure 101,” said Julian Sanchez, an expert in national-security law for the libertarian Cato Institute. “Unless it’s a secret investigation, if you’re conducting an investigation, you interview its subject.”

“He would need to interview anyone who’s a subject of the investigation,” Sanchez added. “That’s Trump, and, at minimum, personnel associated with the campaign.”

“I can’t imagine he would not be interviewed,” said Mark Zaid, a national-security lawyer.

Mueller has been charged to investigate “any matters that arose or may arise directly from the investigation” that the FBI has been conducting into alleged collusion between Trump’s campaign and Russian government officials. That would likely include the allegations from James Comey, who reportedly wrote in a memo that Trump asked him to curtail part of that investigation before firing him.

Like Comey, Mueller knows a thing or two about memos.

Mueller, who became FBI director a week before the 9/11 terror attacks, was a colleague of James Comey during the Bush administration. And one of the most consequential moments in that relationship involves note-taking—a skill Comey has clearly adopted.

As Comey revealed in congressional testimony in 2007, he and Mueller clashed with top Bush White House officials in March 2004 over an effort to reauthorize NSA surveillance. Comey was deputy attorney general at the time—second in command at the Justice Department. Alberto Gonzales, then the White House counsel, and Andy Card, then Bush’s chief of staff, tried to get then-Attorney General John Ashcroft to sign off on the continuation of a warrantless wiretapping program when he was gravely ill in the hospital.

When Comey learned what Gonzales and Card were trying to do, he let Mueller know and then raced to the hospital. He got to the attorney general’s hospital bed while Gonzales and Card were there, and managed to keep him from signing anything. Mueller got to the hospital room after the drama unfolded.

And, like any good FBI hand, Mueller took notes.

In 2007, when Gonzales was attorney general, he testified before Congress that Ashcroft was lucid and talkative on the night of the hospital visit. Comey later gave testimony countering what Gonzales said, saying Ashcroft was clearly sick and distressed. And Mueller’s notes became a pivotal piece of evidence to clear up the disparity, as The Washington Post reported at the time. He turned over a heavily redacted version of those notes to the House Judiciary Committee, showing Gonzales had misinformed the committee.

The news of Mueller’s notes broke on Aug. 17, 2007. Ten days later, Gonzales announced he would resign.

A decade later, Mueller and Comey are again embroiled in a conflict with major consequences for the country. Rod Rosenstein, who has Comey’s old job as deputy attorney general, announced Wednesday that Mueller would take over the investigation, writing that the special counsel could investigate “any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump.”

“Naming somebody like Bob Mueller suggests that they’re serious about this,” said Ron Hosko, who was assistant FBI director for a year under Mueller.

And John Pistole, who also served as an assistant FBI director under Mueller, said Mueller and Comey respect each other’s work.

“I think Jim admires Director Mueller,” he said. “It’s a formidable combination, if you have Bob Mueller and Jim Comey on an issue.”

“In many respects, Bob has been a mentor to Jim in terms of being a federal prosecutor and then FBI director,” Pistole added.

The announcement drew broad bipartisan praise from members of Congress—a disorienting change from the divisive tone in Washington over the past few weeks.

Danforth, who investigated the FBI raid at Waco as a special counsel, told The Daily Beast he thinks it’s a good move.

“If you have the Justice Department doing it itself, you have Donald Trump investigating Donald Trump,” he said.

Among Mueller’s biggest challenges, said Danforth, will be preventing leaks about the investigation that would undermine it.

“The credibility of what we were doing depended on getting all of the information and all of the facts and not just, ‘Here’s today’s news story,’” he said of his time as a special counsel.

That investigation took 14 months and cost $17 million, he noted.

Retired FBI agents who spoke to The Daily Beast also praised the move.

“A lot of old-school agents were not fans of Mueller because we felt like he didn’t respect the work that we had done,” said John Terry, a retired FBI agent who supervised an organized-crime squad. “The feeling was that, after 9/11—‘You guys don’t know what you’re doing, you guys didn’t connect the dots.’ We felt that he disrespected us. But having said that, I think that his integrity and his willingness to make tough decisions speaks for itself, and I think that’s exactly the type of guy to come in. As far as I know, nobody’s going to influence him.”

Another retired FBI agent said Mueller sometimes berated his subordinates in front of each other—a practice that generated resentment toward him and hurt morale.

“He’s very intense,” the retired agent said. “He’s very, very intense. He felt the pressure, and rightfully so, as director when 9/11 occurred.”

“He turned the FBI around, and I give him credit for that,” he added. “He turned us from a crime organization to an intelligence organization, and did it with the agents kicking and screaming at times.”

And Hosko said people who work with Mueller can expect to be pushed—and hard.

“There were no easy days with Bob Mueller,” he said.