Alan Dershowitz, the famed defense lawyer and Harvard Law School professor emeritus, is a lifelong liberal and proud of it. He twice voted in presidential elections for Barack Obama. He’s a friend and supporter of Bill and Hillary Clinton — voted for her in 2016 and even contributed money to her campaign.

He is no fan of President Trump, he says.

Now, however, he’s a hero of the right, a status bearing the imprimatur of no less than Trump himself, who on Monday tweeted his name and called his appearance on Fox and Friends a “must watch . . . with respect to the greatest Witch Hunt in U.S. political history.”

Trump, of course, was characterizing the investigation by special counsel Robert S. Mueller III into the possible collusion between his campaign and Russian operatives to influence the 2016 presidential election.

“I don’t know what has happened to Professor Dershowitz,” conservative talk radio host Rush Limbaugh said in June. “But whatever it is, I like it.”

What has happened to Professor Dershowitz? Nothing, as far as he’s concerned, except that he’s espoused a novel theory that a president, in this case Trump, cannot be guilty of obstructing justice simply for firing the FBI director, even if one of his motives was to shut down an investigation.

As a result, Dershowitz told The Washington Post on Wednesday, he is being shunned by many of his old political allies. His motives are being questioned. And people who used to be his friends just don’t want to hear from him.

“None of my liberal friends invite me to dinner anymore,” he said. “Thanks to Donald Trump, I’ve lost seven pounds. I call it the Donald Trump diet,” he joked.

Even so, Dershowitz says that he’s the same fiery, uncompromising civil libertarian that he has always been.

In that role, he has used his talk-show, celebrity lawyer, Harvard star power to argue that all the people who see Trump’s firing of FBI director James B. Comey as obstruction of justice are dead wrong. The president, he argues, cannot obstruct justice simply for exercising the powers of his office; that is, simply for firing or pardoning someone.

With the term whirling around Washington, a former federal prosecutor explains what to know about the criminal charge of obstruction of justice. (Jenny Starrs/The Washington Post)

He has made his case all over television, in the various columns and commentaries he writes and in the many interviews he has given on the subject. He has made it often and with increasing vehemence even as criticism has mounted.

“I believe the following,” he told The Post. “A president can be charged with obstruction of justice if he does anything unlawful outside the exercise” of his constitutional power as set out in Article II of the Constitution — if he pays hush money, for example, or destroys evidence. “That’s obstruction of justice.”

But “what is not obstruction of justice is a president doing what Article II allows him to do, pardon people, fire people,” such as Comey, whatever the motive. (For a more detailed explanation by Dershowitz, see this interview in Slate.)

If that argument sounds familiar, it’s because it was made last week by Trump’s personal lawyer, John Dowd, who in a statement that shocked many, declared that the “president cannot obstruct justice because he is the chief law enforcement officer under [the Constitution’s Article II].”

That novel interpretation of the law was immediately dubbed the “Dershowitz-Dowd theory.” It was controversial enough that Trump’s White House lawyer, Ty Cobb, hastened to state that it was not a theory adopted by the president and not a defense he would deploy.

Dershowitz’s theory has been roundly condemned and critiqued by a number of legal scholars, most thoroughly in an article by scholars Daniel J. Hemel and Eric A. Posner, in which they wrote that it “crumbles under scrutiny.”

While a few have publicly accepted the validity of at least part of it, Dershowitz concedes that “almost all of my colleagues at Harvard disagree with me.”

He says a number of lawyers and scholars privately accept his argument but are unwilling to say so publicly because they don’t want to do anything that helps Trump. “I would say that 25 times people have either written me, called me, or told me in person and said, ‘You’re right. You’re 100 percent right. Your arguments are solid, but why do you have to say it? Just keep quiet. Don’t help them.’ ”

What’s really upsetting him, he says, is the questioning of his motives and what he describes as a kind of ostracism he has experienced since propounding his ideas on a CNN panel shortly after the firing of Comey. In that appearance, even his former student Jeffrey Toobin appeared stunned by Dershowitz’s argument. “I could not think Alan is more wrong,” Toobin said after Dershowitz stated that Trump “has the right to say” to Comey or anyone else in the executive branch, “you will not investigate Flynn.”

“People have accused me of everything,” Dershowitz told The Post. “Of taking money. … A guy on MSNBC asked me if I was being paid by Trump. Others have asked me if I’m writing a book about it,” he said. “The answer to both is no and no.”

“Everybody’s questioning motive,” he said, with some suggesting he’s jockeying for a seat on the Supreme Court (“I’m 79 years old”) or that he wants to be Trump’s lawyer. None of this is true, he said. “People can’t just accept that I’m saying what I believe and I would be saying the same thing if Hillary Clinton were president.”

His viewpoint “has affected my friendships,” Dershowitz said. “I have a nephew who is just furious at me. He wants to do anything to have this guy impeached or removed from office and he says I’m stopping that. There are people who think — and I’ve been accused of this in print — that I’m the one who put this obstruction argument into the head of Trump and his lawyers, especially since Trump tweeted that he liked my argument.”

Dershowitz said he “got an email today from a very prominent friend — I’m not going to disclose his name because it was a private email — admitting that I’m right and saying ‘My hatred toward Trump blinds me to your truths.’ That was his email. ‘My hatred for Trump blinds me to your truths. Please stop.’

“And then he said to me, ‘Don’t ever send me another tweet that includes an article that you wrote that helps that son of a b‑‑‑‑.’

And “this is a close friend,” Dershowitz said. “The email starts, ‘I love you. It starts ‘I love you but … .”

The reaction, he said, reflects the emotional intensity of his critics when it comes to Trump. “You have to choose sides. Either you’re for Trump or you’re against.”

Dershowitz has been embroiled in heated controversies for his entire career. The only comparable reaction he said he’s gotten is after the acquittal of O.J. Simpson in 1997, when he was part of the “dream team” defending him.

Before the verdict, “it was okay. Everybody’s entitled to a defense. … And then when he was acquitted — surprisingly to everybody, including me — people were furious at me. Really angry.” People sent back copies of Dershowitz’s book, “Chutzpah,” with one person drawing a swastika on it, he said. “I got a letter from a dentist on a dental pad saying ‘I hope your mother has her throat slit the way’ ” Ron Goldman’s throat was slit on the night Simpson’s ex-wife was murdered.

The reaction now is different, he said. “That was emotional hatred. This comes from very smart people.”

“But look, I have a very thick skin,” he said. “It’s upsetting my children. It’s upsetting my wife a little bit. For me, it’s energizing.”

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