WASHINGTON – Turns out, President Trump's feud with Tennessee Republican Sen. Bob Corker isn't over.

Their war of words escalated on Tuesday as the president insisted the prominent Republican senator "couldn't get elected dog catcher" — and Corker described the president as "utterly untruthful."

Trump attacked Corker over Twitter after the chairman of the Foreign Relations Committee defended his previous comment that the White House resembles an adult day care center and criticized his aggressive approach to North Korea.

"Bob Corker, who helped President O give us the bad Iran Deal & couldn't get elected dog catcher in Tennessee, is now fighting Tax Cuts...." Trump tweeted.

Trump then referred to Corker's decision not to seek re-election next year: "Corker dropped out of the race in Tennesse (sic) when I refused to endorse him, and now is only negative on anything Trump. Look at his record!"

Corker — who says Trump did actually offer to support his re-election bid — responded with a zinger: "Same untruths from an utterly untruthful president. #AlertTheDaycareStaff."

Trump hit back again in a pair of tweets.

"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!"

The back-and-forth came hours before Trump and Corker were to attend the weekly Senate Republican policy lunch at the U.S. Capitol.

Prior to the luncheon, Corker offered further critiques of Trump when stopped by reporters on Capitol Hill. He accused Trump of "bullying," "name-calling" and "dividing."

"For young people to be watching ... someone of this mentality ... is something that is debasing to our country," Corker said.

He said he had seen no evolution in Trump's behavior as president. "It appears to me that it's almost devolving."

Earlier, in an appearance on ABC's Good Morning America, Corker said Trump is unnecessarily raising tensions by escalating tensions with North Korea over its nuclear weapons program — and suggested that he let diplomats deal with the problem.

"The president undermines our secretary of State, raises tensions in the area by virtues of the tweets that he sends out and I would just like for him to just leave it to the professionals for a while and see if we can do something that is constructive for our country, the region and the world," Corker said.

The argument between the Republicans isn't necessarily a petty feud. While Republicans have a Senate majority, they control only 52 of the 100 votes. Every vote counts and only a few defectors can deprive the GOP of major legislation, as happened with attempts to repeal and replace President Obama's health care plan.

Trump and Corker have clashed repeatedly, especially after the Tennessean announced he would not seek re-election to a third term.

After a Trump attack on Oct. 8, Corker responded on Twitter: "It's a shame the White House has become an adult day care center. Someone obviously missed their shift this morning."

Later that day, in a New York Times interview, Corker said Trump's rash statements and reckless threats could set the United States "on the path to World War III."

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Corker did not regret either of those statements on Tuesday, telling Good Morning America: “I don’t make comments that I haven’t thought about.”

In addition, Corker has said that Trump did try to talk him into running for the Senate again and offered to help him, but he decided against seeking another term.

Corker also criticized Trump over negotiations on a tax cut bill. The senator questioned a Trump tweet Monday that took one proposal off the table, a call to reduce the amount of money that people can invest in pre-tax 401(k) accounts.

“If you start taking things off the table before you get started, you make that very difficult,” Corker told ABC. “What I hope is going to happen is the president will leave this effort to the tax-writing committees."

Corker also appeared on NBC's Today show, where he questioned the utility of Trump's visit to the GOP policy lunch.

“I think it's fine for him to come over," he told NBC. "I do look at these things as more of a photo op. They're not really about substance, but more power to him.”

Later Tuesday morning, in an interview with CNN, Corker said Trump “has great difficulty with truth on many issues” and that, if he had it to do over, he would not support him for president.

Asked whether he considered Trump a role model for children, Corker replied: “No. Absolutely not.”

When Trump’s presidency is over, “I think the debasement of our nation is what he will be most remembered for,” Corker said. “I think that’s regretful.”

Corker said he doesn’t want his feud with Trump to turn into a daily issue.

“He currently is a person from the executive side that we have to deal with,” Corker said. “And the shame of it is there are some really good people around him. If he would stay out of their way and let them perform, people like (Secretary of State Rex) Tillerson and (Defense Secretary Jim) Mattis and others, we could really make progress on things that really matter greatly to our country.”