To some extent, however, the rift between the two men had been building for months, as Mr. Corker raised doubts about Mr. Trumpâs character and fitness for office. Once a campaign supporter of the president, the senator has become openly derisive of his leadership.
After a report last week that Secretary of State Rex W. Tillerson had once referred to Mr. Trump as a âmoron,â Mr. Corker told reporters at the Capitol that Mr. Tillerson was one of three officials helping to âseparate our country from chaos.â Those remarks were repeated on âFox News Sunday,â which may have prompted Mr. Trumpâs outburst.
In August, after Mr. Trumpâs equivocal response to the deadly clashes in Charlottesville, Va., Mr. Corker told reporters that the president âhas not yet been able to demonstrate the stability nor some of the competence that he needs to demonstrate in order to be successful.â
Mr. Trumpâs feud with Mr. Corker is particularly perilous given that the president has little margin for error as he tries to pass a landmark overhaul of the tax code â his best hope of producing a major legislative achievement in the coming months.
If Senate Democrats end up unified in opposition to the promised tax bill, Mr. Trump would be able to lose the support of only two of the Senateâs 52 Republicans in order to pass it. That is the same challenging math that Mr. Trump and Senate Republican leaders faced in their failed effort to repeal and replace the Affordable Care Act.
Mr. Corker, who is outspoken about the nationâs mounting debt, has already signaled deep reservations about the Republican effort to pass a tax overhaul, saying he would not vote for a tax bill that adds to the deficit.
In addition, Mr. Corker, who leads the Senate Foreign Relations Committee, could play a key role if Mr. Trump follows through on his threat to âdecertifyâ the Iran nuclear deal, kicking to Congress the issue of whether to restore sanctions on Tehran and effectively scuttle the pact.
Republicans could opt to hold off on sanctions but use the threat of them to force Iran back to the negotiating table â a strategy being advocated by Senator Tom Cotton, the Arkansas Republican who is a leading hard-liner on Iran. But that approach could leave the United States isolated, since European allies have made it clear they would rather stick with the deal.
Beyond the Iran deal, Mr. Corkerâs committee holds confirmation hearings on Mr. Trumpâs ambassadorial appointments. Were the president to push out Mr. Tillerson secretary of state â as some expect â Mr. Corker would lead the hearings on Mr. Trumpâs nominee for the post.
Mr. Trumpâs clash with Mr. Corker is somewhat analogous to his rancorous relationship with Senator John McCain, the Arizona Republican who, like Mr. Corker, is winding down his senate career and twice opposed Republican efforts to repeal and replace the Affordable Care Act.
Mr. Trumpâs budget chief, Mick Mulvaney, alluded to Mr. Corkerâs political liberation, saying on âMeet the Pressâ that his decision not to run âsort of unleashes him to do whatever and say whatever he wants.â
A former mayor of Chattanooga, Mr. Corker, 65, has carved out a reputation over two terms in the Senate as a reliable, not overly partisan, Republican, who helped maneuver President Barack Obamaâs divisive nuclear deal with Iran to a vote on the Senate floor. That exposed him to fierce fire from conservatives, who blame him for not blocking the agreement.
Mr. Corker was briefly a candidate to be Mr. Trumpâs running mate in 2016, but he withdrew his name from consideration and later expressed ambivalence about Mr. Trumpâs campaign, in part because he said he found it frustrating to discuss foreign policy with him.
âI donât know that I really have a lot to say,â he said to a reporter in June, adding that he had tried to advise Mr. Trump and was âdiscouraged by the results.â
For much of Mr. Trumpâs byzantine selection process for secretary of state, Mr. Corker was a dark horse. Though he met with Mr. Trump, he drew little of the attention of Mitt Romney, who dined with the president-elect at an expensive Manhattan restaurant and became the object of a very public tug of war between Mr. Trumpâs aides.
Known for his easygoing and affable manner, Mr. Corkerâs positions on foreign policy issues are generally middle-of-the-road for a Republican. But he has shown occasional flashes of vehemence, particularly on subjects that concern him, like human trafficking.
In September 2016, Mr. Corker joined a small group of lawmakers at the residence of former Vice President Joseph R. Biden Jr. for breakfast with Myanmarâs pro-democracy figure and government leader, Aung San Suu Kyi. Afterward, he bluntly faulted her for her reluctance to condemn the mistreatment of Myanmarâs Muslim Rohingya minority.
âWhile we certainly appreciate the work Aung San Suu Kyi has done to ensure a democratic transition in Burma,â he said, âI am somewhat appalled by her dismissive reaction to concerns I raised this morning about the problem of human trafficking in her country.â
But Mr. Corker is remembered most â and vilified by critics â for his role in advancing the Iran nuclear deal. Though not a fan of the agreement â he once accused former Secretary of State John Kerry of having been âfleecedâ in the negotiations with the Iranians â he was instrumental in winning an up-and-down vote on it.
In the end, Republicans â including Mr. Corker himself, who voted against the deal â fell two votes short of the 60-vote threshold needed to pass a resolution killing the six-nation accord.
Republicans are less likely to do that this time, with a fellow Republican in the White House, but Mr. Corkerâs voice will be important to framing how the Senate decides to handle the agreement.