WASHINGTON — Alan Dershowitz arrived at the White House this week expecting to discuss the Middle East. Before long, the president had invited him to an intimate dinner of a ravioli appetizer, guinea hen entree, and, for dessert, fruit compote.

A longtime liberal Harvard professor who says he did not even vote for Donald Trump in 2016 emerged this week as a key Trump whisperer, gaining the president’s ear with his outspoken criticism on Fox News and other venues of Special Counsel Robert Mueller and the FBI.

Dershowitz, in an interview with the Globe Wednesday, would not divulge what was discussed over dinner Tuesday evening. But it’s a good bet the subject of Trump’s unhappiness with the special counsel probe came up, given that this week Trump publicly mused about firing Mueller after the FBI raided the offices of Trump’s private lawyer Michael Cohen. Trump spokeswoman Sarah Huckabee Sanders said the White House believes Trump has the authority to fire Mueller if he sees fit.

Though Dershowitz has frequently complained that Mueller typifies an overzealous prosecutor, he offers this surprise counsel to the president: “I would certainly advise him not to fire anybody,’’ he said in the interview. “Legally, he would have the right to seek the firing of anybody in the executive branch. The court cases are very clear on that. But I would think that would be a mistaken political decision to fire anybody.

“As an American citizen, I’m concerned about what it would do to divide America. I would rather see actions that bring us together than actions that would divide us.’’

If that is what Dershowitz said to Trump on Tuesday night, many mainstream Republicans and members of Congress will be thanking him. Dershowitz has emerged as a confidant at a time when Trump is increasingly isolated in the White House, after the exit of steadying hands including his communications adviser Hope Hicks.

“The president told me he sometimes watches me on television. Sometimes he agrees with me, sometimes he doesn’t,’’ Dershowitz said. “I said ‘Mr. President, you’re free to watch. I’m honored you sometimes watch me.’ ’’

Dershowitz has spent his career at Harvard Law School and has been involved in cases that garnered national attention. He was on the defense team for the O.J. Simpson murder case and helped overturn the conviction of British socialite Claus von Bülow in the murder of his wife. He often rails against prosecutorial overreach and has been a defender of civil liberties.

He has backed Democratic candidates — including, he said, Hillary Clinton in 2016 — but has over the past year developed a closer relationship with Trump. Dershowitz and his wife were dining last year at Trump’s Mar-a-Lago club in Florida — there as guests of Trump’s friend Chris Ruddy, the CEO of the conservative news source Newsmax — when the president came to their table to chat about the Middle East.

On TV, Dershowitz has called the Mueller investigation a “legal colonoscopy,’’ a phrase with surefire appeal to a president who has repeatedly denounced the probe on Twitter as a “WITCH HUNT!’’

Dershowitz wrote a column for The Hill, a Washington-based newspaper, last month headlined “Trump is right: The special counsel should never have been appointed.’’ Trump tweeted the professor’s comments to his 50 million followers. In appearances on Sean Hannity’s program this week, Dershowitz criticized federal law enforcement officials for being too heavy-handed.

“He has lost perspective,’’ he said of Mueller. “I think that happens when overzealous prosecutors are given a target. And the concern now is that there won’t be cooperation. I think we will now see a scorched-earth policy on both sides.’’

Dershowitz said in a column for The Hill on Tuesday that the raid of Cohen’s office could significantly damage attorney-client privilege in other corners of the legal community. “A highly publicized raid on the president’s lawyer will surely shake the confidence of many clients in promises of confidentiality by their lawyers,’’ he wrote.

Dershowitz also contends that Deputy Attorney General Rod Rosenstein should recuse himself from overseeing the Russia probe. Rosenstein wrote the memo that Trump relied on as justification for firing James Comey as FBI director. Rosenstein, who is overseeing the investigation because Attorney General Jeff Sessions recused himself following revelations about his meeting with the Russian ambassador, later appointed Mueller as special counsel.

Dershowitz argues the situation poses a conflict of interest that requires Rosenstein to step aside.

“If I were Trump’s lawyer, the first person I’d call would be Rosenstein. ‘Did you obstruct justice? Did you advise the president to do anything that obstructs justice?’ ’’ Dershowitz said in the interview.

“You can’t be a witness and a prosecutor on the same case,’’ he added. “That’s a basic element of the rule of law.’’

Removing Rosenstein is an emerging argument among conservatives, who are targeting him with more vigor than Mueller, with the idea that it would send a message to the special counsel without the political explosion that could occur if he were fired.

Last month, Dershowitz got into a heated argument with Jeffrey Toobin, who is a former student, during a debate on CNN over whether a special counsel should have been appointed.

“Alan, I don’t know what’s going on with you,’’ Toobin said. “How has this come about that in every situation over the past year you have been carrying water for Donald Trump? This is not who you used to be. . . . What’s happened to you?’’

Dershowitz pointed out instances when he disagreed with Trump, including the president’s proposed ban on immigrants from six Muslim majority countries, and said that he has always been skeptical of appointing a special counsel in almost any instance.

“I’m not carrying his water. I’m saying the exact same thing I said for 50 years. And, Jeffrey, you ought to know that. You were my student,’’ he said. “The fact that it applies to Trump now rather than applying to Bill Clinton is why people like you have turned against me.’’

Dershowitz said the stated reason for the White House meeting Tuesday, planned a week ago as part of a series he’s had with administration officials, was to discuss the Middle East, an issue that Dershowitz has been passionate about for decades.

Since their encounter at Mar-a-Lago, Dershowitz said, he has continued having talks with White House officials.

“It was a complete and total coincidence that it occurred a day after the raid on the office,’’ he said, referring to the FBI’s seizing of materials from Cohen.

He would not get into what was discussed but offered, “The president was in very good spirits, very engaged in discussions about the Middle East.’’

He would not say whether they discussed Mueller.

“I don’t give legal advice to anyone who is not my client, for one very good reason: You can be subpoenaed,’’ Dershowitz said. “And Donald Trump is not my client.’’

If Trump were, Dershowitz said, he would offer this advice: “No pardons, no firing, no tweeting, and no testifying.’’

Matt Viser can be reached at matt.viser@globe.com.