Outgoing Sen. Claire McCaskill Claire Conner McCaskillMomentum growing among Republicans for Supreme Court vote before Election Day Democratic-linked group runs ads in Kansas GOP Senate primary Trump mocked for low attendance at rally MORE (D-Mo.) did not hold back when giving a scathing assessment of the Republican Party and President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE, saying GOP senators privately say Trump is “nuts.”

McCaskill in November lost her reelection bid to Republican Josh Hawley Joshua (Josh) David HawleySenate GOP faces pivotal moment on pick for Supreme Court Renewed focus on Trump's Supreme Court list after Ginsburg's death What Facebook's planned change to its terms of service means for the Section 230 debate MORE and will be leaving Washington in less than two weeks.

In an exit interview with CNN, she said when she speaks privately with Republican senators they tell her how they really feel about Trump.

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"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,' " she told CNN. "But in public if they go after him ... they know they get a primary [challenger], and they know that's tough."

While McCaskill declined to name any specific senators, she did mention Sen. Lindsey Graham Lindsey Olin GrahamSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-S.C.), saying, “I don’t know what happened with Lindsey.”

Graham has aligned himself with Trump on many issues but has recently rebuked the president on his handling of foreign diplomacy decisions, including Trump’s move to pull U.S. troops from Syria.

However, McCaskill acknowledged that the GOP has largely molded itself around Trump.

"This is Donald Trump's Republican Party," McCaskill said. "Make no mistake about it."

Hawley beat McCaskill in Missouri soundly after getting supported and endorsed by Trump. Hawley was the state’s attorney general and filed a lawsuit with other state attorneys general seeking to overturn ObamaCare.

McCaskill, who served two terms in the Senate, has not been shy about speaking her mind in her last few weeks.

She said Trump has done so many things out of the ordinary, that no realizes how crazy some of the actions are anymore.

"I mean, Kanye West was in the Oval Office M-F---ing on live TV," McCaskill said. "I mean, think about that. That is crazy weird. Can you imagine would have happened if that happened during the Obama years? ... The lid would have blown off this place."

McCaskill also gave her opinion of Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellFEC flags McConnell campaign over suspected accounting errors Poll: 59 percent think president elected in November should name next Supreme Court justice Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE (R-Ky.), calling him "a very, very political leader."

"This isn't somebody who is sitting around at night figuring out how he can move the needle on really important policy issues," she claimed. "This is someone who is figuring out how he can win elections, beat Dems like me make sure that Republicans like Cory Gardner Cory Scott GardnerCook Political Report shifts Colorado Senate race toward Democrat Overnight Health Care: US coronavirus deaths hit 200,000 | Ginsburg's death puts future of ObamaCare at risk | Federal panel delays vote on initial COVID-19 vaccine distribution The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting MORE (Colo.) and Thom Tilllis (N.C.) can hold onto their jobs a few years from now."

-Updated 5:11 p.m.