President Trump was pleased with constitutional law scholar Alan Dershowitz’s defense of him over his firing of former FBI Director James Comey, calling the Harvard Law professor’s analysis on Fox News a “must watch” interview.

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

Dershowitz, a lifelong Democrat, said Trump has the constitutional right as president to fire his FBI director.

“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,” Dershowitz said during an interview with Fox News.

“We have precedents that clearly establish that.”

Talk of the president obstructing justice resurfaced after his former national security adviser, retired Lt. Gen. Michael Flynn pleaded guilty to lying to the FBI last week about his conversation with the Russian ambassador.

Trump didn’t help matters by tweeting over the weekend that he knew Flynn lied to the FBI.

“I had to fire General Flynn because he lied to the Vice President and the FBI. He has pled guilty to those lies,” Trump wrote. “It is a shame because his actions during the transition were lawful. There was nothing to hide!”

Democratic Sen. Dianne Feinstein (D-CA) said over the weekend that a Senate investigation into Russia's interference in the 2016 presidential election has revealed possible obstruction.

"I see it in the hyper-frenetic attitude of the White House, the comments every day, the continual tweets. And I see it most importantly in what happened with the firing of Director Comey, and it is my belief that that is directly because he did not agree to ‘lift the cloud’ of the Russia investigation. That’s obstruction of justice,” Feinstein said on NBC’s “Meet the Press.”

But Dershowitz disagreed.

"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," he said.

The famed attorney explained “clearly illegal acts” on the president’s part would need to be proven.

"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, hoping Special Counsel Robert Mueller understands that.

"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."