Real estate mogul and outspoken conservative Donald Trump this week called Fox News contributor Charles Krauthammer a “totally overrated clown” on Twitter after the pundit criticized Trump’s potential 2016 presidential candidacy.

Beginning late Thursday and continuing through the early hours of Friday, Trump ranted against Krauthammer and called him a “dummy” in a series of tweets.

One of the worst and most boring political pundits on television is @krauthammer. A totally overrated clown who speaks without knowing facts — Donald J. Trump (@realDonaldTrump) June 5, 2015

.@krauthammer pretends to be a smart guy, but if you look at his record, he isn’t. A dummy who is on too many Fox shows. An overrated clown! — Donald J. Trump (@realDonaldTrump) June 5, 2015

Dummy political pundit @krauthammer constantly pressed the crazy war in Iraq. Many lives and trillions of dollars wasted. U.S. got NOTHING! — Donald J. Trump (@realDonaldTrump) June 5, 2015

Trump criticized Krauthammer’s book during his angry outburst.

“@krauthammer: On sale today. Things That Matter in paperback. With a new section on the Obama years. Book sucks! — Donald J. Trump (@realDonaldTrump) June 5, 2015

Trump’s Twitter rage was prompted by comments Krauthammer made Thursday during an appearance on the Fox News show “Special Report with Bret Baier,” where he mocked Trump’s low favorability ratings.

“It’s just a tremendously interesting poll,” Krauthammer said, of a poll showing Republicans whom respondents would never vote for. “It is led by Donald Trump with a deserved 59 percent.”

“Do you have to add the ‘deserved’?” host Bret Baier asked.

“Well ‘cause I know I’m gonna get, he’s gonna say how sad it is that I’m saying all these things, but, you know, this is an open forum and we have free speech,” Krauthammer said. “Yes, a well deserved, I would say an impressive 59 percent.”

Trump is expected to make an announcement about his potential presidential run on June 16.

Watch the video below, from Fox News. Krauthammer’s comments come at about the 3:20 mark.

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h/t The Hill