In Alan Dershowitz’s telling, he’s stayed the same. It’s everyone else who’s changed.

The retired Harvard law professor, whose decades-long career made him one of the nation’s most recognizable liberal advocates, is now playing a surprising role: one of President Donald Trump’s staunchest defenders. In an interview on Friday, I began to ask him about his newfound role as an “advocate” for Trump. He quickly interrupted me.

“I’m not an advocate for President Trump, let’s be clear,” he told me. “I’m an advocate for civil liberties. I’d be making the exact same point for Hillary Clinton if she were elected president.”

Dershowitz isn’t alone among legal scholars in questioning aspects of the Russia investigation. There’s debate over whether it would be constitutional to indict a sitting president and whether Trump committed obstruction of justice. But few law professors can match Dershowitz’s name recognition, his long history of supporting Democrats, or his frequent appearances on cable television. This has made him a valuable asset for Trump as he wages a barely disguised war on special counsel Robert Mueller’s inquiry.

Dershowitz’s defense of the president has bewildered some of his friends and colleagues. In March, Jeffrey Toobin, a New Yorker staff writer and CNN senior legal analyst, confronted Dershowitz on TV about “carrying water” for Trump. “This is not who you used to be,” Toobin told him. “And you are doing this over and over again in situations that are just obviously ripe with conflict of interest. And it’s just, like, what’s happened with you?”

“I’m not carrying his water,” Dershowitz replied. “I’m saying exactly the same thing I’ve said for 50 years.” He echoed this response when I asked why he thought liberals were criticizing him so much. “There’s such a hyper-partisan passion to get President Trump that anything that’s seen as trying to help President Trump is seen as supporting Trump,” he said.

Dershowitz’s latest critique of the investigation came after FBI agents searched Michael Cohen’s office earlier this month. Legal experts widely viewed the raid as a bad sign for the president’s longtime personal lawyer. To seek a search warrant for any lawyer’s office, federal prosecutors have to get approval from high up in the Justice Department. Raiding the office of the president’s personal attorney apparently prompted even greater scrutiny: Deputy Attorney General Rod Rosenstein signed off on the search, according to The New York Times.

The American Civil Liberties Union had no complaint with the raid on Cohen’s office in principle. “That the warrant was issued is not a sign that the attorney-client privilege is dead,” a staff attorney wrote for the organization. “It is, on the contrary, a sign that the rule of law is alive.” Dershowitz, who once served on the organization’s board, viewed the remarks as hypocrisy. “The ACLU not only remains silent, but they came out in support of the search of a lawyer’s office for the first time in history,” he told me.

From Dershowitz’s perspective, the Russia investigation is symptomatic of a broader civic ailment that affects both sides of the aisle: wielding criminal investigations in a politicized manner to harm one’s opponents. This includes partisan-driven probes like the investigation into Clinton’s use of a private email server or the conspiracy theory surrounding the Uranium One deal, as well as the two-year federal inquiry into whether the Trump campaign colluded with Russia to meddle in the 2016 election to hurt Clinton.

“I don’t believe collusion is a crime,” he told me, noting that collusion doesn’t exist as such in the federal criminal statutes. (Other legal experts have concluded it would violate campaign-finance laws.) He also rejected the idea that Trump’s pardoning of top officials would be an impeachable offense. “The best evidence is George H. W. Bush, who pardoned Caspar Weinberger to stop the investigation into Iran-Contra,” he said, for which President Bush faced no consequences.

Weinberger, who served as President Ronald Reagan’s secretary of defense during the Iran-Contra scandal, was one of six officials who received pardons from Bush in 1991 that short-circuited an independent-counsel probe. Many now fear that Trump could use the pardon power to aid Cohen, Michael Flynn, or Paul Manafort, and thereby prevent Mueller from using plea deals to obtain damaging evidence and testimony. Trump’s pardon of Scooter Libby last week only intensified those fears.

I asked Dershowitz if he was worried that his legal interpretations amounted to impunity for public officials. “The Constitution provides that no senator or congressman can be prosecuted for what they say on the floor,” he told me. Judges also can’t be sued for what they do in their official capacity, he added. “So it shouldn’t be surprising that the Constitution has provided some breathing space for the three branches of government” when using their official powers.

Dershowitz once denounced the impeachment proceedings for Bill Clinton in 1998 as “sexual McCarthyism.” So are there circumstances in which he thinks it would be proper to impeach a president? “Only if the constitutional criteria are met: bribery, treason, or other high crimes and misdemeanors,” he replied. That’s a high bar to pass. The president’s exercise of his lawful constitutional powers—such as firing an FBI director for dubious reasons—wouldn’t qualify, he said. A more appropriate remedy, he told me, are for Americans to exercise their power through the electoral process.

That Dershowitz, a prominent Jewish American public intellectual, would speak up in Trump’s defense is jarring, as he appears to recognize. “When I defended the right of Nazis to march in Skokie, my mother told me, ‘You have to take sides, you’re either with the Jews or the Nazis,’” he told me. “And I said, ‘Mom, I’m on the side of civil liberties.’” In his mother’s defense, he added, she didn’t go to law school, and many of his current sparring partners don’t have the same excuse.

One of them is Nancy Gertner, who spent seventeen years as a federal judge in Massachusetts and is currently a law professor at Harvard. Earlier this month, Dershowitz told a radio-show host that Mueller had “kept four innocent people in prison for many years” to protect Boston mobster Whitey Bulger’s identity as an FBI informant. Bulger’s decades-long relationship with the FBI is controversial and embarrassing for the bureau. Gertner, who knows the case better than just about anyone, spoke up in Mueller’s defense.

“I was the federal judge who presided over a successful lawsuit brought against the government by two of those men and the families of the other two, who had died in prison,” she wrote in the Times. “Based on the voluminous evidence submitted in the trial, and having written a 105-page decision awarding them $101.8 million, I can say without equivocation that Mr. Mueller, who worked in the United States attorney’s office in Boston from 1982 to 1988, including a brief stint as the acting head of the office, had no involvement in that case. He was never even mentioned.”

Dershowitz, unswayed, told the Boston Globe that Gertner’s “legitimate partisan concerns” about Trump had led her astray. “The idea that Mueller bears no responsibility for this tragedy?” he told the newspaper. “I think that’s the kind of statement someone would make only if they were a strong anti-Trump partisan.” (Gertner declined a request for an interview.)

Toobin, a former student of Dershowitz, is another sparring partner. In an interview last Friday, he struck a more diplomatic tone than his cable-news clash with him in March. “I think Alan is a serious civil libertarian,” he told me, “and his natural inclination is to question the exercise of prosecutorial power, and in that respect, his behavior is consistent with his lifelong commitments.”

Trump’s case isn’t the only one raising red flags for Dershowitz. “I’m saying the same thing about the Benjamin Netanyahu case,” he told me. “I’ve been saying the same thing in the Israeli press.” The comparison is apt: Netanyahu faces multiple investigations for corruption and official misconduct, weakening his domestic political standing. Channeling Trump, the Israeli prime minister has even described the inquiries as a “media witch hunt.”

That investigation combines the Dershowitz’s two major subjects of interest. He’s one of the highest-profile American commentators on Israeli politics, typically in Israel’s defense. (He authored a book in 2003 titled The Case for Israel, to refute frequent criticisms of the country and its policies.) In December, Trump formally recognized Jerusalem as Israel’s capital and set in motion the U.S. embassy’s move from Tel Aviv to the holy city. Dershowitz praised the controversial policy shift in a Fox News op-ed, which he said reversed a “cowardly decision” made by President Barack Obama in 2016.

“President Trump deserves praise for restoring balance in negotiations with Israel and the Palestinians,” he wrote. “It was President Obama who made peace more difficult. It was President Trump who made it more feasible again.”

Dershowitz told me he diverges with the Trump administration on many other issues. “I’m very much opposed to the president’s travel ban,” he said. “I’ve very much opposed to the free availability of guns in school. I’m opposed to the death penalty.” Indeed, capital punishment is where the contrast is clearest. Trump is not only a supporter of the death penalty, but an enthusiast of it. As a Supreme Court clerk in the early 1960s, Dershowitz helped launch the legal war in the 1960s that led to its brief abolition a decade later.

That work eventually saved hundreds of men from constitutionally and legally flawed executions. It also kicked off a legal career that saw him speak out for defendants as varied as the Deep Throat film producer on free-speech grounds in the 1970s, Austrian aristocrat Claus von Bulow in an attempted-murder case in the 1980s, the O.J. Simpson murder trial in the early 1990s, and now, in an unofficial (and apparently pro bono) capacity, President Donald Trump. Through all this time, Dershowitz told me, his principles have stayed the same.

“I go back half a century in what I’m doing,” he said. “I’ve done nothing different.”