FILE - In this Aug. 16, 2017, file photo, Sen. Bob Corker, R-Tenn., speaks to the Sevier County Chamber of Commerce in Sevierville, Tenn. Always one to speak his mind, Corker’s new free agent status should make President Donald Trump and the GOP very nervous. The two-term Tennessee Republican isn’t seeking re-election. And that gives him even more elbow room to say what he wants and vote how he pleases over the next 15 months as Trump and the party’s top leaders on Capitol Hill struggle to get their agenda on track (AP Photo/Erik Schelzig, File)
FILE - In this Aug. 16, 2017, file photo, Sen. Bob Corker, R-Tenn., speaks to the Sevier County Chamber of Commerce in Sevierville, Tenn. Always one to speak his mind, Corker’s new free agent status should make President Donald Trump and the GOP very nervous. The two-term Tennessee Republican isn’t seeking re-election. And that gives him even more elbow room to say what he wants and vote how he pleases over the next 15 months as Trump and the party’s top leaders on Capitol Hill struggle to get their agenda on track (AP Photo/Erik Schelzig, File) Credit: Erik Schelzig

WASHINGTON — An enraged President Donald Trump and a prominent Republican senator who fears the country could be edging toward “chaos” engaged in an intense and vitriolic back-and-forth bashing on social media Sunday, a remarkable airing of their party’s profound rifts.

In political discourse that might once have seemed inconceivable, the GOP’s foreign policy expert in the Senate felt compelled to answer his president’s barbs by tweeting: “It’s a shame the White House has become an adult day care center. Someone obviously missed their shift this morning.”

Trump earlier had laid bare his perceived grievances against retiring Sen. Bob Corker, R-Tenn., in a series of stinging tweets that 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.

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.

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.”

Corker, a fiscal hawk, is holding the GOP’s feet to the fire on tax legislation, declaring that he’ll oppose any measure that increases the national debt by a single cent. Republicans hold a narrow, 52-seat majority in the Senate, and just three defections would torpedo the top priority in their partisan push.

Corker delivered a rebuke of the Trump White House after the president’s provocative tweets undermined 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.