President Donald Trump flew into a rage Tuesday morning after Republican Senator Bob Corker harshly criticized him during an impromptu interview. “Sen. Corker is the incompetent head of the Foreign Relations Committee, & look how poorly the U.S. has done. He doesn't have a clue as the entire World WAS laughing and taking advantage of us. People like liddle' Bob Corker have set the U.S. way back. Now we move forward!” he tweeted, minutes after the retiring Tennessee lawmaker told CNN that Trump has “great difficulty with the truth” and that it’s “unfortunate that our nation finds ourselves in this place.”

Asked about his relationship with the president, Corker said that Republicans had attempted multiple times to “try and create some kind of aspirational approach, if you will, to the way that he conducts himself,” but that all such efforts had failed. “I don't think that that's possible. He's obviously not going to rise to the occasion as president.” Trump responded by immediately proving his point.

Corker’s comments, and Trump’s apoplectic response, were the latest in an escalating feud between the two men that exploded earlier this month when Corker said the White House had become “an adult day-care center” and warned that the president was putting the country “on the path to World War III.” Earlier Tuesday, the senator had derided the president and suggested during an interview with Good Morning America that the White House stay out of the Republican effort to re-write the tax code. “I would just like him to leave it to the professionals for a while and see if we can do something that’s constructive,” Corker, who sits on the powerful Budget and Foreign Relations committees, said. “If you start taking things off the table before you get started, you make it very difficult.”

On the heels of Corker’s first interview, Trump dismissed the senator’s criticism as retaliation for his refusal to endorse him—a claim Corker has denied—and accused him of playing a key role in the passage of the Obama-era Iran nuclear accord, despite the fact that the Foreign Relations chairman voted against the deal. He also said that Corker, who has been a vocal opponent of any tax plan that adds to the deficit, “will now fight Tax Cuts plus!”

Corker boldly pushed back on those claims Tuesday. “Nothing that he said in his tweets today were truthful nor accurate,” the senator said. ”He knows it, and the people around him know it. I would hope that the staff over there would figure out ways of controlling him, when everything he said today was absolutely untrue.” He added that Trump encouraged him four times to seek re-election in Tennessee and told him that he would endorse him.

Corker went on to further attack Trump’s integrity. “I don’t know why he lowers to such a low, low standard and debases our country in the way that he does. But he does,” he told CNN. When asked whether he regrets supporting Trump during the election, Corker responded, “Let’s just put it this way: I would not do that again,” adding, “No way.”