WASHINGTON (AP) — A powerful Republican senator cast the president of his own party as a man-child who could set the U.S. "on the path to World War III" as the two engaged in an intense and vitriolic back-and-forth bashing, a remarkable airing of their party's profound rifts.

In political discourse that might once have seemed inconceivable, Sen. Bob Corker, the chairman of the Foreign Relations Committee, felt compelled to answer his president's barbs on Sunday by tweeting: "It's a shame the White House has become an adult day care center. Someone obviously missed their shift this morning."

In an interview Sunday with The New York Times, Corker said Trump could set the U.S. "on the path to World War III" with threats toward other countries. Corker also said Trump acted as if he was on his old reality-TV show and that he concerned the senator, adding: "He would have to concern anyone who cares about our nation."

Corker also said his concerns about Trump were shared by nearly every Senate Republican, the paper reported.

In a series of stinging tweets earlier in the day, Trump contended Corker:

—Was "largely responsible for the horrendous" Iran nuclear deal, which the Democratic Obama administration negotiated and Corker considered badly flawed. The senator also tried to require that President Barack Obama submit the accord to Congress for approval.

—Intended to obstruct the White House agenda, though he offered no evidence for saying he expected Corker "to be a negative voice."

—"Begged" for Trump's endorsement in his 2018 re-election, then opted against seeking a third term when Trump declined, showing the senator "didn't have the guts to run." The Associated Press reported that Trump, in a private meeting in September, had urged Corker to run. Corker's chief of staff, Todd Womack, said Sunday that Trump called Corker last Monday to ask that he reconsider his decision to leave the Senate. Trump "reaffirmed that he would have endorsed him, as he has said many times," the aide said.

—Wanted to be secretary of state, and "I said 'NO THANKS,'" said Trump, who picked Exxon Mobil's Rex Tillerson for that Cabinet post. Corker, the Senate Foreign Relations Committee chairman, was mentioned as a possible pick after the election.

Trump added another tweet Sunday evening: "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!"

Corker always had been one to speak his mind, and even before Sunday's verbal volleys, his new free agent status promised to make Trump and the party nervous. Already, there was the prospect of even more elbow room to say what he wants and to vote how he pleases over the next 15 months as Trump and the party's leaders on Capitol Hill struggle to get their agenda on track.

Corker's comments drew a rebuke Monday from White House Counselor Kellyanne Conway, who said on "Fox & Friends" that she finds "tweets like this to be incredibly irresponsible." She added that the president's door is always open to speak with lawmakers privately.

The top Republican in the Senate, who has been the target of Trump's ire, deflected questions about the escalating fight between Corker and Trump.

"Sen. Corker is a valuable member of the Senate Republican caucus and he's also on the Budget committee and a particularly important player as we move to the floor on the budget next week and he's an important part of our team," Majority Leader Mitch McConnell, R-Ky., said Monday during a stop in Hazard, Kentucky.

Not long before Trump's tweeting, White House budget director Mick Mulvaney said on NBC's "Meet the Press" that "it's going to be fun to work" with Corker, "especially now that he's not running for re-election, because I think it sort of unleashes him to do whatever — and say whatever — he wants to say."

In his interview with the Times, Corker said: "Look, except for a few people, the vast majority of our caucus understands what we're dealing with here," adding that "of course they understand the volatility that we're dealing with and the tremendous amount of work that it takes by people around him to keep him in the middle of the road."

Corker delivered a rebuke of the Trump White House after the president's tweets scoffing at Tillerson's diplomatic efforts to resolve the crisis with North Korea. Corker said Tillerson, along with Defense Secretary Jim Mattis and White House chief of staff John Kelly, are "those people that help separate our country from chaos."

And Corker will be at the center of what may be a stormy debate over the future of the Iran agreement. Trump's hostility toward the deal has stoked concerns he's aiming to dismantle the international accord despite Europe's objections. Corker is opposed to scrapping the agreement outright.

"You can only tear these things up one time," Corker said. "It might feel good for a second. But one of the things that's important for us is to keep our allies with us, especially our Western allies."

Corker is the latest Republican to face Trump's wrath. The president in recent months has lit into McConnell over the failure of the GOP to repeal and replace Obama's health care law, and specifically targeted Sens. John McCain, R-Ariz., and Lisa Murkowski, R-Alaska, for their opposition to GOP health legislation.

Corker, 65, announced last month that his second, six-year term would be his last.

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Associated Press writers Adam Beam in Hazard, Kentucky, and Andrew Taylor in Washington contributed to this report.

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Contact Richard Lardner on Twitter at http://twitter.com/rplardner