WASHINGTON — Senate Democrats on Monday secured the votes necessary to filibuster the Supreme Court nomination of Judge Neil M. Gorsuch, presaging a bitter confrontation this week that threatens to further unravel a chamber where bipartisanship and decorum have eroded for years.
The show of solidarity from the minority came as Republicans advanced Judge Gorsuch’s nomination in the Judiciary Committee, clearing the way for his consideration on the Senate floor.
Republicans vowed Monday to confirm him by the end of the week. The implication was not subtle: If they must change longstanding rules to bypass the filibuster, elevating President Trump’s selection on a simple majority vote, they will not hesitate.
“We have no alternative,” Senator Orrin G. Hatch of Utah, the longest-serving Republican in the Senate, said alongside his Judiciary Committee colleagues after a party-line vote, 11 to 9.
It was the beginning of what both parties consider a seminal week on Capitol Hill, likely to fundamentally reshape the way the Senate conducts its business.
Though lawmakers have long deployed the filibuster — a procedural device that allows for continued debate to block or delay a vote — to suit their circumstances, Supreme Court confirmations have been viewed as another matter, insulated at least somewhat from the body’s most partisan passions.
Under current rules, Republicans cannot break the filibuster if fewer than 60 senators vote to move the nomination to an up-or-down Senate vote. That would require eight Democrats to join the 52-seat Republican majority. As of Monday evening, only four Democrats had announced support for an up-or-down vote.
Judge Gorsuch’s fate will depend on whether Republicans follow through on plans for the so-called nuclear option, as Mr. Trump has urged, to circumvent the filibuster for a Supreme Court pick.
“The Republicans are free actors,” Senator Chuck Schumer of New York, the Democratic leader, said Monday, urging a withdrawal of the nomination if Judge Gorsuch cannot earn 60 votes. “They can choose to go nuclear or they can sit down with Democrats and find a way forward that preserves the grand traditions of this body.”
Such was the theme of Monday’s proceedings: a series of meditations on grand traditions, a resignation to their imminent demise and an insistence that the other side was to blame.
During the committee vote, senators took turns lamenting the state of the institution they serve, although none pledged to buck their own party on either the Democratic filibuster or the Republican push for a rule change.
What comes next, it appears, is a slow-motion dismantling of senatorial standards and practice, scheduled for demolition over several days.
“This is a new low,” Senator Mitch McConnell of Kentucky, the Republican majority leader, said of the likely filibuster, “but not entirely surprising.”
Of course, Democrats identify Mr. McConnell as the chief purveyor of new lows. From the beginning, the Gorsuch nomination has been shadowed, in large measure, by Judge Merrick B. Garland, whom President Barack Obama nominated in March 2016 after the death of Justice Antonin Scalia the month before. Mr. McConnell led Republicans in refusing to even consider the nomination during a presidential election year.
But Democrats insist that their opposition to Judge Gorsuch is not about payback. They have cited his record on workers’ rights and his degree of independence from Mr. Trump and conservative groups like the Federalist Society, among other concerns.
Perhaps no member sounded as pained on Monday as Senator Patrick J. Leahy, Democrat of Vermont and the Senate’s longest-serving member.
He first argued that the treatment of Judge Garland had convinced Judge Gorsuch that “this committee is nothing more than a partisan rubber stamp,” allowing the nominee to evade straightforward questions during his hearings.
Mr. Leahy suggested that Mr. McConnell had no qualms about “forever damaging the United States Senate.”
And he wondered aloud how the Capitol had become so unrecognizable to him, after 42 years.
“I cannot vote solely to protect an institution when the rights of hard-working Americans are at risk,” Mr. Leahy said. “Because I fear that the Senate I would be defending no longer exists.”
Republicans have in turn faulted Democrats for what they call two escalations of hostilities: a series of filibusters against judicial nominees under President George W. Bush and a vote in 2013, when Democrats controlled the Senate, to bar filibusters for the president’s appeals court and executive branch nominees. That shift left the filibuster for Supreme Court nominations untouched.
Supporters of Judge Gorsuch have appeared incredulous that the Senate — whose members approved Justice Scalia unanimously and did not use a filibuster for even some fiercely contested nominees like Justice Clarence Thomas — could come undone over a judge they view as plainly qualified and uncontroversial.
“It’s pathetic,” Mr. Hatch said, “that they’re so stupid that they picked somebody of his quality and ability” to oppose.
Senator Charles E. Grassley, Republican of Iowa and the committee’s chairman, accused Democrats of searching in vain for credible reasons to vote against “a judge’s judge.”
Senator Ted Cruz, Republican of Texas, pressed the case that Judge Gorsuch’s nomination carried a “superlegitimacy” because voters last year knew that the next president would get to fill the seat. (Before the election, he had suggested trying to leave the seat open indefinitely if Hillary Clinton won.)
Yet even some Republicans who planned to support a rule change if necessary said they worried about what would come of it.
Senator Lindsey Graham, Republican of South Carolina, predicted that a simple-majority threshold for Supreme Court confirmations would lead to the elevation of future judges who are “more ideological, not less.” Every Senate race, he added, would effectively become a referendum on the Supreme Court.
“This is going to haunt the Senate, it’s going to change the judiciary, and it’s so unnecessary,” Mr. Graham said after the vote.
Though some Democrats have expressed concerns, in public and private, about pushing ahead with a filibuster, they are also aware of their political hand: The party’s progressive base has called on lawmakers to oppose Mr. Trump at every turn, reminding them of the extraordinary dynamics at play.
Senator Richard Blumenthal, Democrat of Connecticut, linked his vote opposing Judge Gorsuch, at least in part, to the current investigations into connections between Mr. Trump’s orbit and Russia.
“It is about the constitutional crisis that may well be looming,” he said, arguing that Judge Gorsuch had not demonstrated sufficient independence from Mr. Trump. Mr. Blumenthal added that the prospect of the Supreme Court needing to enforce a subpoena against the president was “far from idle speculation.”
Even lighter fare on Monday could not coax consensus from committee members. At one point, Mr. Grassley asked the senators how they would like to manage their lunch schedule: a half-hour break for everyone or an uninterrupted hearing with senators peeling off one by one to eat.
The room appeared split. “Could the majority cater this lunch?” asked Senator Al Franken, Democrat of Minnesota. A few Republicans raised their hands to convey a desire to keep going.
Senator Dianne Feinstein of California, the committee’s top Democrat, smiled slightly, her hands clasped. The committee, she said quietly, could not even agree on lunch.