For weeks, the outcome of the Senate fight has appeared preordained, even as members lamented its inevitability as a low moment for the chamber. In recent days, faint rumblings of a deal to avert the clash had faded almost entirely.
Republicans have argued that changing the rules to push through the nomination was their only option, seeking to shift responsibility for blowing up the Senate’s longstanding practices to the Democrats. Allowing the filibuster to succeed, they said, would cause more damage than overriding Senate precedent to ensure it fails.
“This is the latest escalation in the left’s never-ending judicial war, the most audacious yet,” Senator of Kentucky, the majority leader, said after describing Democratic opposition in the past to Judge Robert H. Bork and Justice Clarence Thomas. “And it cannot and it will not stand. There cannot be two sets of standards: one for the nominees of the Democratic president and another for the nominee of a Republican president.”
But Democrats had shown no signs of forsaking their filibuster plans all week. That has pleased their most progressive voters, who have preached resistance to Mr. Trump at every opportunity, and supplied the minority party with perhaps its loudest megaphone so far under the new president.
Many Democrats remain furious over the treatment of Judge Merrick B. Garland, President Barack Obama’s nominee for the seat left vacant with the February 2016 death of Justice Antonin Scalia. Republicans refused to even consider Judge Garland during the presidential election year, a fact Mr. McConnell has not dwelled on during public statements about the history of Republican behavior under Democratic presidents.
“There must have been a hacking into his computer,” Senator Richard J. Durbin, Democrat of Illinois, said of Mr. McConnell on Thursday from the Senate floor, “because he can’t print the name Merrick Garland to include in the speech.”
At the same time, critics of Judge Gorsuch say they have identified ample reasons to oppose him, chafing at the suggestion that Democrats are merely seeking payback. They have cited concerns over Judge Gorsuch’s record on workers’ rights and whether he will be reliably independent from Mr. Trump and conservative groups like the Federalist Society, among other issues.
“The more we learned about Judge Gorsuch’s record, the more we didn’t like,” said Senator Chuck Schumer of New York, the Democratic leader.
Republicans have likewise taken particular pains to highlight what they deem escalations of hostilities by Democrats through the years. These include efforts to block judicial nominees under President George W. Bush and the 2013 rule change, when Democrats barred other filibusters.
For the body’s most veteran lawmakers in both parties, the moment has been trying.
The longest-serving senator, Patrick J. Leahy, Democrat of Vermont, had initially said he was disinclined to embrace a filibuster. But on Wednesday, he railed against his Republican colleagues from the Senate floor.
“They have no interest in playing by the rules,” he said. “They prefer to break them.”
Senator of Utah, the longest-serving Republican, said the episode had bothered him “as much as any battle that we’ve had” through his four decades in the chamber.
But when considering a judge whom conservatives view as deeply qualified and uncontroversial, Mr. Hatch said he had no choice. The Supreme Court filibuster would have to go.
“I won’t be happy about that,” he said. “But I will do it.”