WATCH: MSNBC segment explodes after Dershowitz calls lawyer Richard Painter 'un-American and a liar'
Alan Dershowitz and Richard Painter on MSNBC, composite image.

Harvard Law School professor emeritus Alan Dershowitz was shut down on MSNBC Saturday after launching a bizarre tirade against former chief White House ethics lawyer Richard Painter.

Dershowitz is a prominent defender of President Donald Trump, the original topic of the segment with host David Gura, before it descended into chaos.

While answering a question about Robert Mueller interviewing longtime Trump confidante Tom Barrack, Dershowitz said the special counsel, "has a mixed reputation, when I was in Boston with regard to four innocent people who spent their life and two of them died in jail."

Painter immediately interrupted Dershowitz.

"That is not true, that's not true, you can't say that about him, do not -- that is not true professor," Painter blasted. "That's a lie, do not assault his reputation, that's just not true. He's a good man."

In response to Painter defending the special counsel, Dershowitz began his tirade of personal attacks.

"Let me talk about your reputation," Dershowitz began. "He has lied repeatedly about me and other people, Trump supporters."

"You have no right to go on national television and say things that are false about Robert Mueller," Painter continued. "It's not about you."

"You say I know nothing about Israel," Dershowitz replied. "You condemned me for that."

"This has nothing to do with Israel," Painter shot back. "You lied about Robert Mueller. This has nothing to do with Israel. This has to do with you're assaulting the reputation of Robert Mueller, a good American."

Dershowitz then escalated the rhetoric by declaring that the former White House official was un-American.

"He may be, but you're not, sir!" Dershowitz charged. "You're a liar and you've lied repeatedly about my background and expertise."

"I didn't say anything about your background, I said you lied about Robert Mueller's reputation in Boston," Painter reminded Dershowitz.