WASHINGTON — Senate Democrats secured enough votes to filibuster the nomination of Judge Neil Gorsuch to the U.S. Supreme Court on Monday, making it all but certain that Republicans will change the rules of the U.S. Senate to ensure his confirmation later this week.

Democratic opposition to Gorsuch has been building for days, and four more senators announced on Monday that they would vote against him. That gives Democrats the requisite 41 senators to block a procedural vote and compel President Trump and Republicans either to withdraw Gorsuch’s nomination or to change Senate rules to eliminate the 60-vote requirement.

“This is a new low,” Senate Majority Leader Mitch McConnell, R-Ky., said in response to Democratic opposition. But he also reiterated his vow that Gorsuch will be confirmed by Friday despite the likelihood of a filibuster. That’s because McConnell is prepared to invoke what is known as the “nuclear option” – a change in rules allowing Supreme Court nominees to be confirmed with a simple-majority vote. With 52 seats, Republicans would then have enough votes to secure Trump’s first selection for the high court.

The procedural vote known as cloture has long set the Senate apart from the House of Representatives – and it has long been hailed by members of the upper chamber for requiring bipartisan cooperation, and forcing consensus, on major legislation or confirmation votes.

If that step is eliminated, the Senate is “headed to a world where you don’t need one person from the other side to pick a judge,” warned Sen. Lindsey Graham, R-S.C. “And what does that mean? That means the judges are going to be more ideological, not less. It means that every Senate seat is going to be a referendum on the Supreme Court … The damage done to the Senate is going to be real.”

McConnell won’t be the first to go nuclear, however. Now-retired Sen. Harry Reid, D-Nev., first invoked the option in 2013 when he was majority leader, allowing non-Supreme Court presidential appointments to be confirmed with a simple majority.

And McConnell will probably face more pressure to eliminate the 60-vote requirement in other cases – on budget bills, for instance, or for that matter on any legislation at all. If that happens, the need for bipartisan cooperation could disappear entirely from the Senate.

Graham’s comments came as the Senate Judiciary Committee voted to refer Gorsuch’s nomination to the full Senate, which is expected to begin debating the pick on Tuesday. The procedural step that Democrats have the votes to block is expected by Thursday, but if McConnell at that point seeks a rules change – which would succeed with a simple majority – it would start the clock for a final confirmation vote some time on Friday.

The outcome of the Judiciary Committee’s vote was never in doubt – Republicans hold a majority of seats on the panel, and Gorsuch was approved on a party-line vote. But the testy hearing foreshadowed what is likely to be a combative floor debate over the merits of Trump’s selection and the way both parties have behaved during years of feuding over the makeup of the federal court system.

Sens. Dianne Feinstein, D-Calif., Patrick Leahy, D-Vt., Christopher Coons, D-Del., and Mark Warner, D-Va., indicated on Monday that they would oppose Gorsuch and vote against cloture – the motion to end a filibuster that is required to hold a final up-or-down confirmation vote.

During an hours-long committee hearing, Leahy criticized Gorsuch’s answers during his marathon confirmation hearing as “excruciatingly evasive.” He said that a GOP move to end filibusters of Supreme Court nominees would damage the Senate, but he argued that he had to vote his conscience, even if it pushes Republicans to change the rules.

“I cannot vote solely to protect an institution when the rights of hard-working Americans are at risk,” he said, “because I fear that the Senate I would be defending no longer exists.”

Sen. John Cornyn, R-Texas, shot back, blaming Democrats for years of partisan bickering over judicial nominees that they say started when President George W. Bush made several nominations for federal court vacancies earlier this century.

“I disagree with those who somehow say this is the end of the Senate as we know it,” Sen. John Cornyn, R-Texas, said. “This is a restoration of the status quo ante before our Democratic colleagues directed this artificial 60-vote requirement.”

Senate Minority Leader Charles Schumer, D-N.Y., dismissed Republican attempts to blame Democrats for the change.

“I’m sure we could trace it all the way back to the Hamilton-Burr duel,” he quipped.

“The answer isn’t to change the rules,” he added. “The answer is to change the nominee.”

In a sign that there is almost no hope of ending the impasse without a rules change, Sen. John McCain, R-Ariz. – who helped quell previous fights about judicial nominees – said that this time, he is standing with fellow Republicans.

“I have to. I have no choice,” he told reporters, explaining that he must vote for a change “because we need to confirm Gorsuch.”

McCain has been part of fruitless attempts to reach a bipartisan agreement in recent days, including consultations with Coons and Sen. Joe Manchin III, D-W. Va., late last week. McCain told reporters that he was part of a similar conversation on Monday, but he did not elaborate.

Manchin is one of three moderate Democrats who plan to vote for Gorsuch, and with Republicans, to end the filibuster. Manchin and the other two moderates, Joe Donnelly, D-Ind., and Heidi Heitkamp, D-N.D., have been the focus of a $10 million ad campaign by the conservative Judicial Crisis Network, which is pressuring Democrats facing reelection next year in states that Trump won in November to vote for Gorsuch.

Meanwhile, Sen. Michael Bennet, D-Colo., on Monday became the fourth Democrat to say he would join Republicans in trying to end the filibuster. But in a sign of the incredible political pressure he faces as he votes on a nominee from his home state, Bennet did not state whether he plans to support or oppose Gorsuch. He has also faced pressure from JCN to back Gorsuch. So far he is the only Democratic senator not up for reelection in 2018 opposing the filibuster.

Carrie Severino, JCN’s chief counsel and policy director, said on Monday that in the face of “unprecedented obstruction by Democrats, Republicans now have no choice but to invoke the “constitutional option” – also known as the nuclear option – to confirm Gorsuch.

Gorsuch was nominated by Trump on Jan. 31 and spent weeks privately meeting with senators and preparing for his confirmation hearing. He was questioned by the Judiciary Committee last month for almost 20 hours over three days, answering nearly 1,200 questions and later sending about 70 pages of answers to written follow-up questions, according to a team of White House officials assisting with his nomination.

As of Friday, Gorsuch had met with 78 senators – all but some of the most conservative and liberal lawmakers whose votes are likely to fall along party lines. Three first-term Democratic senators, Catherine Cortez Masto, Nev., Tammy Duckworth, Ill., and Kamala Harris, Calif., complained that they were unable to get a face-to-face meeting with the nominee or offered the opportunity.

This week’s anticipated change in Senate procedure dates to 2013, when Democrats, angered by Republican opposition to then-President Obama’s nominees end filibusters of executive branch and lower-court nominees, prompting Republicans to warn that there might one day be retribution.

“Changing the rules is almost inevitable; it’s only a question of when,” said Norm Ornstein, a longtime congressional expert and resident scholar at the American Enterprise Institute.

Ornstein warned that with Republicans set to extend the filibuster ban to Supreme Court nominees, they may soon face pressure to end filibusters of legislation to keep major health-care and tax reform bills passed by the GOP-led House from stalling in the more closely-divided Senate.

McConnell, R-Ky., “will resist the change in some cases because it’s in his interest not only when he’s in the minority again but also to be able to rely on Democrats when the House sends you crazy things,” Ornstein said. “And because it’s not clear they have the 51 votes necessary to change the rules for filibusters on legislation.”

But McConnell said on NBC’s “Meet the Press” on Sunday that “I don’t think the legislative filibuster is in danger.”

Schumer, appearing on the same program, agreed: “I don’t think there’s any thirst to change the legislative rules. Most Democrats and most Republicans have served in both the minority and majority and know what it means.”