Democratic senator reveals that Republicans in Congress privately believe Trump is 'nuts'
President Donald Trump (Shutterstock).

An outgoing Democratic senator revealed in her CNN exit interview that some of her Republican colleagues privately disparage President Donald Trump in conversations with her.

Sen. Claire McCaskill (D-MO) said that when she's been alone with Senate Republicans, they've intimated that the president is unfit to serve.

"Now they'll tell you, if it's just the two of you, 'The guy is nuts, he doesn't have a grasp of the issues, he's making rash decisions, he's not listening to people who know the subject matter,'" McCaskill told CNN. "But in public if they go after him ... they know they get a primary, and they know that's tough."

The Missouri Democrat who lost to Trump-backed Republican Josh Hawley during the general election in November told the network that regardless of what they say in private, members of the GOP who refuse to push back against the president will be judged "harshly" by history.

Though she refused to name names, she did admit to CNN that South Carolina Republican Sen. Lindsey Graham's relationship to the president was strange.

"It's kind of weird to me," McCaskill said. "I don't know what happened with Lindsey."