WASHINGTON • The relationship between President Donald 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.
What was once an uneasy governing alliance has curdled into a feud of mutual resentment and sometimes outright hostility, complicated by the position of Mr McConnell's wife, Ms Elaine Chao, in Mr Trump's Cabinet, according to more than a dozen people briefed on their imperilled partnership.
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 mobilising for their defence.
The rupture between them comes at a highly perilous moment for Republicans, who face a number of urgent deadlines when they return to Washington next month.
Congress must approve new spending measures and raise the statutory limit on government borrowing within weeks of reconvening, and Republicans are hoping to push through an elaborate rewrite of the federal tax code.
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. In a series of tweets this month, Mr Trump criticised Mr McConnell publicly, then berated him in a phone call that quickly devolved into a profane shouting match.
During the call, the President accused Mr McConnell of bungling the healthcare 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 last year's election.
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.
He even made sharper comments in private, describing the President as entirely unwilling to learn the basics of governing, musing about whether Mr Trump will be in a position to lead the party into next year's elections and beyond.
But, for the moment, Mr McConnell appears to be far more secure in his position, and perhaps immune to coercion from the White House. Republicans are unlikely to lose control of the Senate next year, and Mr Trump has no allies in the Senate who have the appetite to take on Mr McConnell.