The relationship between President Trump and Senator Mitch McConnell, the majority leader, has disintegrated to the point that they have not spoken to each other in weeks, and Mr. McConnell has privately expressed uncertainty that Mr. Trump will be able to salvage his administration after a series of summer crises.
.. Angry phone calls and private badmouthing have devolved into open conflict, with the president threatening to oppose Republican senators who cross him, and Mr. McConnell mobilizing to their defense.
.. A protracted government shutdown or a default on sovereign debt could be disastrous — for the economy and for the party that controls the White House and both chambers of Congress.
Yet Mr. Trump and Mr. McConnell are locked in a political cold war.
.. Don Stewart, a spokesman for Mr. McConnell, noted that the senator and the president had “shared goals,” and pointed to “tax reform, infrastructure, funding the government, not defaulting on the debt, passing the defense authorization bill.”
.. During the call, which Mr. Trump initiated on Aug. 9 from his New Jersey golf club, the president accused Mr. McConnell of bungling the health care issue. He was even more animated about what he intimated was the Senate leader’s refusal to protect him from investigations of Russian interference in the 2016 election, according to Republicans briefed on the conversation.
.. Mr. McConnell has fumed over Mr. Trump’s regular threats against fellow Republicans and criticism of Senate rules, and questioned Mr. Trump’s understanding of the presidency in a public speech. Mr. McConnell has made sharper comments in private, describing Mr. Trump as entirely unwilling to learn the basics of governing.
..In offhand remarks, Mr. McConnell has expressed a sense of bewilderment about where Mr. Trump’s presidency may be headed, and has mused about whether Mr. Trump will be in a position to lead the Republican Party into next year’s elections and beyond
..“When it comes to the Senate, there’s an Article 5 understanding: An attack against one is an attack against all,” said Senator Lindsey Graham, Republican of South Carolina, who has found himself in Mr. Trump’s sights many times, invoking the NATO alliance’s mutual defense doctrine.
..Some of them blame the president for not being able to rally the party around any version of legislation to repeal the Affordable Care Act, accusing him of not knowing even the basics about the policy. Senate Republicans also say strong-arm tactics from the White House backfired, making it harder to cobble together votes and have left bad feelings in the caucus.
..White House aides told Senator Shelley Moore Capito, a Republican from the state whose support was in doubt, that she could only accompany him on Air Force One if she committed to voting for the health care bill. She declined the invitation, noting that she could not commit to voting for a measure she had not seen
.. Senator Lisa Murkowski of Alaska told colleagues that when Mr. Trump’s interior secretary threatened to pull back federal funding for her state, she felt boxed in and unable to vote for the health care bill.
.. But Mr. Hoffman predicted that Mr. McConnell would likely outlast the president.
“I think he’s going to blow up, self-implode,” Mr. Hoffman said of Mr. Trump. “I wouldn’t be surprised if McConnell pulls back his support of Trump and tries to go it alone.”
.. An all-out clash between Mr. Trump and Mr. McConnell would play out between men whose strengths and weaknesses are very different. Mr. Trump is a political amateur, still unschooled in the ways of Washington, but he maintains a viselike grip on the affections of the Republican base. Mr. McConnell is a soft-spoken career politician, with virtuoso mastery of political fund-raising and tactics, but he had no mass following to speak of.
.. Roger J. Stone Jr., a Republican strategist who has advised Mr. Trump for decades, said the president needed to “take a scalp” in order to force cooperation from Republican elites who have resisted his agenda. Mr. Stone urged Mr. Trump to make an example of one or more Republicans, like Mr. Flake, who have refused to give full support to his administration.
.. The president should start bumping off incumbent Republican members of Congress in primaries,” Mr. Stone said. “If he did that, Mitch McConnell and Paul Ryan would wet their pants and the rest of the Republicans would get in line.”
.. But Mr. McConnell’s allies warn that the president should be wary of doing anything that could jeopardize the Senate Republican majority.
“The quickest way for him to get impeached is for Trump to knock off Jeff Flake and Dean Heller and be faced with a Democrat-led Senate,” said Billy Piper, a lobbyist and former McConnell chief of staff.