Senator Bob Corker, the Republican chairman of the Foreign Relations Committee, called the White House "an adult day care centre" after President Donald Trump attacked him in a morning Twitter tirade.
Setting off an extraordinary squabble between two leaders of the same party, Trump alleged in a trio of tweets that Corker "begged" him for his endorsement, did not receive it and decided to retire because he "didn't have the guts" to run for re-election next year.
In response, Corker tweeted, "It's a shame the White House has become an adult day care center. Someone obviously missed their shift this morning."
By alienating Corker, Trump risks further endangering his legislative agenda. As chairman of the Foreign Relations Committee, Corker would be a leading voice on Capitol Hill determining the future of the Iran nuclear deal, should Trump "decertify" the agreement and punt to Congress a decision about whether to restore sanctions against Iran.
Corker also sits on the Senate Finance Committee and looks to play a key role in the upcoming debate over taxes. The senator already has expressed some concerns with the Trump administration's proposal on tax cuts.
Trump's public lashing of Corker comes after the senator made headlines last week when he starkly suggested that the national security team provides the president with needed adult supervision. In a remarkable statement, Corker told reporters that Secretary of State Rex Tillerson, Defense Secretary Jim Mattis and White House Chief of Staff John F Kelly "are those people that help separate our country from chaos".
Trump, who has little tolerance for public criticism and prides himself on counterpunching those who cross him, fired off a trio of tweets Sunday morning attacking Corker, who announced last month that he plans to retire and not seek re-election in 2018.
Trump tweeted, "Senator Bob Corker 'begged' me to endorse him for re-election in Tennessee. 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.' He is also largely responsible for the horrendous Iran Deal! 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!"
A Republican congressional official familiar with Trump and Corker's recent conversations disputed each of the claims the president made in his tweets. Trump called Corker early last week and asked him to reconsider his decision not to seek re-election, according to this official, who spoke on the condition of anonymity because of the sensitivity of the private conversations. The official said the president also reaffirmed that he would have endorsed Corker had he decided to run again - which, the official added, was not the first time that Trump had extended such an offer of support.
Corker was a prominent supporter of Trump's 2016 campaign, and Trump considered him a potential running mate and secretary of state. Corker was one of only a few senators to develop a personal relationship with Trump and his family, but tensions between the two men flared over the summer.
In August, Corker criticised Trump's handling of the deadly white-supremacist rally in Charlottesville, Virginia, saying, "The president has not yet been able to demonstrate the stability nor some of the competence that he needs to demonstrate in order to be successful".
Then, as now, Corker became a subject of Trump's ire. In response to the senator's "stability" and "competence" comments, Trump tweeted, "Tennessee not happy!"
Corker is not the only Republican senator to come under attack from the presidential bully pulpit. In recent months, Trump has gone after Senate Majority Leader Mitch McConnell, and senators Lindsey Graham, John McCain and Jeff Flake, with cutting and sometimes personal insults.
Republican lawmakers have voiced exasperation that Trump is spending his time attacking senators he will need as allies if he hopes to pass any signature legislation, such as the tax-cut plan his administration has been trumpeting.
Mick Mulvaney, director of the Office of Management and Budget, said on Sunday that he enjoys working with Corker and that the senator feels free to speak his mind now that he is not seeking re-election.
"I think it's going to be fun to work with him, especially now that he's announced 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," Mulvaney said Sunday on NBC's Meet the Press.