"Unfortunately I think world leaders are very aware that much of what he says are untrue," he told CNN's Manu Raju. "I don't know why he lowers himself to such a low standard. It debases our country."

Asked if he regrets supporting Trump's 2016 campaign, Corker responded, "Let's just say this: I would not do it again," smiling and grabbing Raju's shoulder.

Corker responded with a quick "no" to a question about whether he considered Trump to be a good role model for children.

Corker also denied that Trump refused to support his reelection bid. He said Trump asked him at least four times to reconsider his decision not to run.

"The president has great difficulty with the truth," he said.

Trump in several tweets responding to Corker's earlier comments on NBC repeated his claim that Corker decided not to run for reelection after Trump refused to endorse him “and now is only negative on anything Trump. Look at his record!”

“Isn't it sad that lightweight Senator Bob Corker, who couldn't get re-elected in the Great State of Tennessee, will now fight Tax Cuts plus!” he tweeted.

Trump added that the “incompetent” Senate Foreign Relations Committee chairman “helped President [Obama] give us the bad Iran Deal & couldn't get elected dog catcher in Tennessee.”

The president also blamed the senator for what he said was the U.S.’s diminished standing in the world before he took office.

“The entire World WAS laughing and taking advantage of us,” Trump tweeted. “People like liddle' Bob Corker have set the U.S. way back. Now we move forward!”

In the "Today" interview, Corker said Trump’s involvement in Congress’s effort to change the tax code will make it harder to pass a bill.

“Tax writing committees in the Senate and the House are going to be laying out the $4 trillion in loophole closings that need to take place,” Corker told NBC. “Hopefully the White House will step aside and let that occur in a normal process.”

The blow-up happened just hours before Trump was scheduled to attend the Senate GOP’s weekly luncheon on Capitol Hill, an event Corker described as a “photo op.”

Corker said it’s “fine” if the president wants to attend the lunch but said he should generally give lawmakers space to craft tax legislation.

“I think that that's the best way for us to have a success,” he said.

The incident highlighted how Trump’s tense relationship with influential Republican lawmakers could complicate his effort to score a win on taxes.

Corker sits on the Senate Budget Committee and is a key vote on tax legislation. Trump and Senate GOP leaders can only afford to lose two votes on a tax overhaul and still pass it.

The Tennessee senator has said he will not support a plan that blows a major hole in the budget deficit. But his deteriorating personal relationship with Trump could also factor into his decision.

Corker has been withering in his criticism of Trump since announcing his plan to retire, which has freed him of having to win support from Trump's base for a reelection bid.

Earlier this month, he referred to the White House as an “adult day care center” and has expressed concern that Trump could lead the U.S. into “World War III.”

“When you have the kind of issue we’re dealing with in North Korea ... when you kneecap that effort, you really move our country into a binary choice which could lead to a world war,” Corker said of Trump on NBC.

“I want him to support diplomatic efforts, not to embarrass and really malign efforts that are underway to try to get some kind of diplomatic solution here, and I think most people would agree with that,” he added.

- This report was updated at 10:30 a.m. EST