President Trump on Tuesday slammed former CIA Director John Brennan as "a very bad guy" after he criticized the president for his remarks at a joint press conference a day earlier with Russian leader Vladimir Putin.

"I think Brennan is a very bad guy, and if you look at it, a lot of things happened under his watch. I think he's a very bad person," Trump told Fox News' Tucker Carlson in an interview from Helsinki, following his first bilateral summit with Putin.

Brennan was one of several former intelligence officials who savaged the president on Monday for refusing to hold Putin accountable for Russian cybercrime against the U.S. during their joint appearance. Trump told reporters during the 45-minute press conference that he was unsure why Moscow would have been behind several attacks on U.S. cyber infrastructure and state voting operations during the 2016 election.

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"Donald Trump's press conference performance in Helsinki rises to and exceeds the threshold of 'high crimes [and] misdemeanors,'" Brennan tweeted shortly after the press conference ended. "It was nothing short of treasonous. Not only were Trump's comments imbecilic, he is wholly in the pocket of Putin."

The former top intelligence official added in an interview with NBC Tuesday that Trump was guilty of "aiding, abetting, [and] giving comfort to an enemy."

Trump walked back some of his comments in a tweet Monday afternoon, as he was en route back to Washington. After contradicting conclusions reached by his own Director of National Intelligence Dan Coats, he reiterated that he has "great confidence in my intelligence people," but believes it is important to "get along" with U.S. adversaries like Russia.