President Trump on Sunday ripped increasingly vocal critic Sen. Bob Corker, saying the Tennessee Republican gutlessly dropped his re-election bid after begging for the Trump endorsement he never received.

“Corker ‘begged’ me to endorse him,” Trump said in a string of tweets. "I said ‘NO’ and he dropped out (said he could not win without my endorsement). He also wanted to be secretary of state, I said ‘NO THANKS.’ ... Hence, I would fully expect Corker to be a negative voice and stand in the way of our great agenda. Didn't have the guts to run!”

Corker fired back minutes later, by tweeting: “It's a shame the White House has become an adult day care center. Someone obviously missed their shift this morning.”

Later in the afternoon, Trump tweeted: “Bob Corker gave us the Iran Deal, & that's about it. We need HealthCare, we need Tax Cuts/Reform, we need people that can get the job done!”

Trump’s attack followed Corker saying last week, amid reports that Secretary of State Rex Tillerson will resign, that Tillerson, Defense Secretary James Mattis, and White House Chief of Staff John Kelly “are those people that help separate our country from chaos.”

Corker Chief of Staff Todd Womack on Sunday disputed Trump's portrayal of the endorsement issue.

“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 told Fox News.

Trump and Corker appeared to have a good relationship early in Trump’s roughly first eight months in the White House, even playing golf together in June with retired NFL quarterback Peyton Manning.

However, that relationship appears to have fractured, at least publicly, in August, when Corker criticized Trump’s handling of the violent Charlottesville protests, in which an alleged white supremacist fatally struck a woman with a car.

Corker said Trump has yet to demonstrate “the stability nor some of the competence” needed to be successful.

Trump on Sunday, in a separate tweet, argued Corker supported the Iran nuclear deal brokered by the previous Obama administration that Trump argues Iran is violating.

“He is also largely responsible for the horrendous Iran Deal!” Trump tweeted.

Fox News' Jason Donner contributed to this report.