MSNBC's Joe Scarborough on Monday said President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE doesn't realize how much damage he did to his presidency when he attacked Sen. Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump MORE (R-Tenn.).

“This is the thing he doesn’t understand — I mean this, the president is so out of it, he doesn’t understand,” Scarborough said.

“That if you attack Bob Corker, a guy who started a business on his own, became unbelievably successful in his 30s, has always been a success, a mayor, two-term senator."

Corker isn't "scared" of the president, Scarborough said.

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"He’s got nothing to lose. The damage that Donald Trump did additionally to his presidency yesterday is unspeakable," Scarborough said, adding that Trump has lost a vote on tax reform.

"If impeachment does come up, I wouldn't be surprised if Bob Corker and John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE and Susan Collins Susan Margaret CollinsJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally Momentum growing among Republicans for Supreme Court vote before Election Day MORE and Lisa Murkowski Lisa Ann MurkowskiMomentum growing among Republicans for Supreme Court vote before Election Day Collins: President elected Nov. 3 should fill Supreme Court vacancy Barrett seen as a front-runner for Trump Supreme Court pick MORE and Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE and all of these Republicans that he's going after, if he's, again, not sealing his own fate," he said.

His comments come after Trump feuded with Corker this weekend, taking aim at the Tennessee Republican over Twitter.

Trump said Corker begged him to endorse his Senate bid, but Trump declined the request.

“Senator Bob Corker ‘begged’ me to endorse him for re-election in Tennessee. I said ‘NO’ and he dropped out (said he could not win without my endorsement),” Trump said.

“He also wanted to be Secretary of State, I said ‘NO THANKS.’ He is also largely responsible for the horrendous Iran Deal!”

Corker's chief of staff, Todd Womack, on Sunday pushed back against Trump's claims.

"The president called Senator Corker on Monday afternoon and asked him to reconsider his decision not to seek reelection and reaffirmed that he would have endorsed him, as he has said many times," Womack said.

Corker said in a New York Times interview that Trump's threats to other countries could put the U.S. "on the path to World War III."