President Donald Trump urged his Twitter followers Monday to watch the interview with Harvard Law School professor emeritus Alan Dershowitz on Fox News’ “Fox & Friends” to glean further insight into the “greatest witch hunt in U.S. political history.”

Dershowitz, a liberal who supported 2016 Democratic presidential nominee Hillary Clinton, responded to speculation from congressional Democrats that special counsel Robert Mueller is building a case for obstruction of justice against Trump. In particular, Dershowitz responded to comments made by Sen. Dianne Feinstein (D-Calif.) on Sunday on NBC’s “Meet the Press.” Feinstein, a member of the Senate Judiciary Committee, said, “I think what we’re beginning to see is the putting together of a case of obstruction of justice.”

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“But there’s never been a case in history where a president has been charged with obstruction of justice for merely exercising his constitutional authority. That would cause a constitutional crisis in the United States,” Dershowitz said.

“And Sen. Feinstein simply doesn’t know what she’s talking about when she says it’s obstruction of justice to do what a president is completely authorized to do under the Constitution,” Dershowitz added.

The Harvard professor argued that Trump had the constitutional authority to fire former FBI Director James Comey and weigh in on the Justice Department’s investigation into former national security adviser Michael Flynn. Flynn pleaded guilty to one count of lying to the FBI after Mueller slapped him with the charge Friday.

Many liberals hoped Flynn’s guilty plea and the questions surrounding Trump’s abrupt firing of Comey back in May would surpass the probe into Russia’s 2016 U.S. presidential election interference — and lead to a definitive obstruction of justice case against the president.

“If Congress were ever to charge him with obstruction of justice for exercising his constitutional authority under Article II, we’d have a constitutional crisis,” Dershowitz said. “You cannot charge a president with obstruction of justice for exercising his constitutional power to fire Comey and his constitutional authority to tell the Justice Department who to investigate, who not to investigate.”

Noting that “we have precedents that clearly establish that” fact from other presidents, Dershowitz said Trump would have needed to commit “clearly illegal acts” in order to be charged with obstruction of justice in Mueller’s probe and in congressional investigations.

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Dershowitz also responded “of course not” when asked if Trump’s wish for the Justice Department to quickly wrap up its Russia probe constituted obstruction of justice, as some Democrats argue.

“The president has the authority to speak to Congress, to tell Congress what he wants to do. And Congress has the power to say no. We have separation of powers,” Dershowitz said. “You can’t have obstruction of justice by each party under separation of powers exercising their authority.”

Although many of Trump’s critics pointed to Flynn’s guilty plea as evidence that Mueller’s obstruction of justice case was building steam, Dershowitz argued that Trump’s decision not to pardon Flynn at this point in time “is very good evidence that there’s no obstruction of justice going on here.”

The president approved of Dershowitz’s arguments, urging Americans to watch the interview.

“A must watch: Legal Scholar Alan Dershowitz was just on @foxandfriends talking of what is going on with respect to the greatest Witch Hunt in U.S. political history. Enjoy!” Trump tweeted.

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