But that does not mean other Senate Republicans will rush to the microphones to second Mr. Corker’s sentiments. In an interview with The New York Times on Sunday, Mr. Corker responded to a series of Twitter attacks on him by Mr. Trump. He said that the president was running the White House like it was “a reality show” and with bellicose threats that could set the nation “on the path to World War III.” Mr. Corker added that “every single day at the White House, it’s a situation of trying to contain him.”
Other Republican lawmakers, while privately nodding their heads, remained conspicuously silent on Monday morning, and many Senate Republicans no doubt were relieved not to be in session this week in Washington, where they would be intercepted in the hallways of the Capitol by reporters asking them to comment on Mr. Corker’s remarks.
“While it may really bother other Senate Republicans and it’s unnerving that one of their own is being attacked, most aren’t retiring and know they must still work with the White House in order to accomplish legislative goals like tax reform or eventually answer to frustrated voters,” said Ron Bonjean, a former top aide to Senate Republican leaders.
Mr. Trump has grown frustrated by Senate Republicans as legislation to repeal President Barack Obama’s health care program has been repeatedly blocked, lashing out at Senator Mitch McConnell of Kentucky, the party leader, for not getting the job done. He has also engaged in open conflicts with Senators John McCain and Jeff Flake of Arizona, Lindsey O. Graham of South Carolina and Lisa Murkowski of Alaska, among others.
Mr. Trump’s former chief strategist, Stephen K. Bannon, acting in what he says is the president’s interest, is organizing a rebellion against the Republican establishment and recruiting candidates to challenge incumbent senators in primaries next year. Vice President Mike Pence’s chief of staff has talked about a “purge” of Republicans who are not loyal to Mr. Trump.
For their part, Senate Republicans have pushed back on occasion. Almost unanimously, they and their counterparts in the House passed legislation over Mr. Trump’s objections mandating sanctions on Russia and limiting the president’s ability to lift them on his own.
They also stood against him when he engaged in a protracted public campaign against his own attorney general, Jeff Sessions, a former colleague of theirs in the Senate, warning him that if he fired Mr. Sessions they would not confirm a successor and acting to prevent him from using his recess appointment power to install a replacement without their consent.
“Guys like Bob Corker, I think, have reached the point where it’s like, ‘Can we not pretend the emperor is not naked? Can we not pretend the emperor is not unstable in a way that we should’ve understood very, very clearly more than a year or two years ago?’” Charlie Sykes, a former conservative talk show host and author of “How The Right Lost Its Mind,” said on CNN on Sunday.
As chairman of the Foreign Relations Committee, Mr. Corker could single-handedly block the confirmation of a new secretary of state should Mr. Trump push out his embattled chief diplomat, Rex W. Tillerson, and he could bottle up other appointments. He would presumably play a key role in any decision on whether to tear up the Iran nuclear deal. And as a longtime deficit hawk, he could also become a challenge for Mr. Trump as the president seeks to pass deep tax cuts that would add hundreds of billions of dollars to the national debt.
Mr. Corker’s public break with the president was a long time in coming. Mr. Trump considered Mr. Corker as a candidate for secretary of state after last year’s election but was said to have told associates that the 5-foot-7 senator was too short. Mr. Corker expressed concern shortly after the inauguration that Mr. Trump was a “wrecking ball” to American foreign policy but he largely tempered his criticism in hopes of helping to steer the nation’s first president to serve without any political or military background.
By last week, that hope was clearly gone. As Mr. Tillerson publicly denied he was considering resignation without denying that he had once called the president a “moron” — he let a spokeswoman deny it later — Mr. Corker volunteered that the secretary of state and two other officials were the only thing that “separate our country from chaos.”
Mr. Trump responded over the weekend by calling Mr. Corker “a negative voice” who “didn’t have the guts to run” for another term. Mr. Corker fired back on Twitter by saying “the White House has become an adult care center” and “someone obviously missed their shift.” He followed up with the Times interview.
The White House complained that Mr. Corker had been “insulting,” as Kellyanne Conway, the president’s counselor, put it on Monday morning. “I find tweets like this to be incredibly irresponsible,” she told Fox News. “It adds to the insulting that the mainstream media and the president detractors — almost a year after this election they still can’t accept the election results. It adds to their ability and their cover to speak about the president of the United States in ways that no president should be talked about.”
Mr. Corker, who may have found the no-guts tweet insulting, has plenty of Republicans agreeing with his point of view. But the ones who have acknowledged that publicly are those like former Senator Trent Lott of Mississippi, the onetime Republican leader in the Senate, who when asked by Politico how Mr. Trump was doing replied, “Not great. Too many problems with disasters and Congress.”
Mr. Lott, of course, is not running again. “Do most senators have their doubts about the president?” asked John Feehery, a longtime Republican congressional aide now working as a lobbyist in Washington. “That’s probably true, but also largely irrelevant. He’s the president, and they have to find ways to get stuff done with him. Otherwise, they face the wrath of the voters — something Bob Corker no longer worries about.”