Alan Dershowitz—a liberal Harvard law professor and ardent backer of Hillary Clinton—has emerged as one of the Russia probe’s most vocal critics.

He’s likened the investigation to a KGB hunt, and special counsel Bob Mueller to a notoriously obsessed sailor. It’s made him a Fox News fixture, and that has left some of his counterparts in the legal world baffled and skeptical. But those close to Dershowitz say his vociferous criticism of Mueller’s investigation is the opposite of surprising—and that Mueller and Dershowitz have a history.

That’s according to Harvey Silverglate, a criminal defense attorney who has worked with Dershowitz over the years. The two men once represented Jeffrey MacDonald, who was convicted decades ago of murdering his wife and two daughters and who still maintains his innocence. Silverglate and Dershowitz tried to get MacDonald a new trial. As part of that effort, said Silverglate, they met with Mueller at the Justice Department headquarters in downtown Washington, D.C.

This meeting came in the early ’90s—Silverglate didn’t recall the exact year—when Mueller headed the Justice Department’s Criminal Division. They wanted him to ask the judge who convicted MacDonald to vacate that conviction because of problems with evidence. A report from the time said Dershowitz argued government agents had conspired to frame MacDonald.

“Mueller opens up the meeting with the following line, which was so seared into my memory that I will never forget it,” Silverglate told The Daily Beast. “He looks at us—Alan Dershowitz and me—and says, OK, gentlemen, I just want to say: Criticism of the bureau is a non-starter.’”

But criticizing the FBI was exactly what Dershowitz and Silverglate had come to do.

“Alan and I both walked away in a little bit of shellshock,” Silverglate continued, “understanding that there were things to Mueller that were more important than facts, more important than truth, more important than the erroneous conviction of an innocent American, and that is, the reputation of the FBI and his relationship with the FBI.”

Dershowitz told The Daily Beast he recalls working on the MacDonald case with Silverglate but doesn’t specifically recall that conversation. He didn’t question Silverglate’s account.

As Mueller’s probe of alleged Russian interference in the 2016 election has gained momentum, Dershowitz has become a staple of conservative media. On Aug. 20, he told New York Republican billionaire radio host John Catsimatidis that Mueller’s probe threatens American democracy.

“The idea of trying to create crimes just because we disagree with [Trump] politically, and target him, really endangers democracy,” he said, according to The Hill. “[It] reminds me of what the head of the KGB said to Stalin: ‘Show me the man, and I will find you the crime.’”

And last month on Fox & Friends, Dershowitz compared Mueller and his team to Captain Ahab from Moby Dick.

“They’re determined to get that white whale,” he said.

Dershowitz has also criticized Mueller for hiring lawyers who have contributed to Democratic politicians. And he recently released a new book, Trumped Up: How Criminalization of Political Differences Endangers Democracy. Critics say he’s a Trump shill. He says that’s laughable.

“Please put on the record that I am not defending him, that I am only focusing on the issues,” he said. “And the issues this time happen to come out largely on his side—but, by the way, not always.”

Some suspect Dershowitz’s advocacy goes beyond his television appearances. A person familiar with the president’s legal affairs said there are concerns Dershowitz has talked about legal affairs with Trump.

Dershowitz told The Daily Beast this isn’t true. He said he and the president have spoken, but never privately. He said the two men spoke at Mar-a-Lago once when Dershowitz dined there with Newsmax CEO Chris Ruddy, a mutual friend of the two. Trump came over to their table and chatted with them about the travel ban, according to Dershowitz. Trump said he wanted to try to enforce the first version of the travel ban, which federal courts had struck down. Dershowitz said he told the president that would be a bad idea.

“Then he took me aside and said, ‘I want to talk to you about the peace prospects in the Middle East because you know Netanyahu,’” Dershowitz said. “I said, ‘Look, Mr. President, I didn’t vote for you, but on Israel and the Middle East, I am passionately concerned with that and I’m happy to help, 24/7.”

Dershowitz said he later met with Jason Greenblatt, Trump’s envoy for Israel-Palestinian negotiations, and that he also met with Mahmoud Abbas shortly before the Palestinian Authority president met with Trump at the White House. And he said he criticized Trump for not making Elliott Abrams—a foreign policy adviser to George W. Bush—the next deputy secretary of state.

Besides Ruddy, Dershowitz and the president share a number of friends and acquaintances, including Patriots owner Bob Kraft. The two men met years ago in Kraft’s suite at a Patriots game, he said.

“I liked him,” Dershowitz said. “He was very nice, he was very affable. We talked football.”

Dershowitz and Trump also both know Jeffrey Epstein, the convicted pedophile who has long been friendly with Bill Clinton, too. Trump once praised Epstein’s social life, noting he likes women “on the younger side.” Epstein was one of Dershowitz’s clients. And he isn’t the most controversial person Dershowitz has defended; the attorney also represented O.J. Simpson.

Publicly, Dershowitz is never one for understatement. Take his recent comments about Antifa, the far left group:

“Antifa is a radical anti-American, anti-free market, communist, socialist, hard, hard-left censorial organization that tries to stop speakers on campuses,” he told the hosts of Fox & Friends—reportedly Trump’s favorite TV show—on Tuesday morning.

He taped that hit from Martha’s Vineyard, where he spends the summers.

“I’m not getting very many invitations to dinner at Martha’s Vineyard,” Dershowitz said wryly. “My life can always be judged by the dinner invitations. They went down to zero when I defended O.J. Simpson, and they’re down considerably now.”

But his cable-news invitations are through the roof.

“There’s a big difference between inviting you to dinner and inviting you to speak, because I do draw crowds,” he said. “Whether or not people like me or don’t like me, nobody has ever accused me of being boring.”

They do accuse him of being opportunistic and intellectually dishonest. Renato Mariotti, a former federal prosecutor who practices law in Chicago, told The Daily Beast he believes Dershowitz’s defense of the president is so terrible it must be in bad faith.

“All of the arguments that are made by Dershowitz appear to me to be highly misleading, and I think that he has enough experience and knowledge as a lawyer to know better,” he said. “For that reason, I’ve concluded that Alan Dershowitz is not giving neutral legal analysis but is instead trying to score political points. I think he’s being disingenuous.”

Deshowitz vigorously disputes that.

“Many serious scholars have told me they agree with these arguments,” he said. “They are certainly serious and are likely to be given serious consideration by any court. Any defense attorney who failed to raise them would be guilty of ineffective assistance of counsel.”

Norm Eisen, the chair of Citizens for Responsibility and Ethics in Washington, sometimes spars with Dershowitz on cable news and on Twitter. And like many of the most prominent legal figures in Washington, he was once one of Dershowitz’s students at Harvard Law.

“Agree or disagree, he’s absolutely consistent in advocating for the narrowest possible reasonable application of criminal law and of the importance of not politicizing it,” Eisen said.

Silverglate added that Dershowitz doesn’t mind the kind of spats that have drawn scorching criticism from fellow Democrats.

“We don’t have friends on the right, we don’t have friends on the left,” he said. “And we manage.”