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WASHINGTON (AP) — Democrats have secured the votes to block President Donald Trump’s Supreme Court nominee under current rules, putting the Senate on a partisan collision course over confirming Neil Gorsuch to a lifetime appointment that could reverberate for decades.

Debate over the 49-year-old appellate judge gets under way in the full Senate on Tuesday, with Republicans and Democrats bitterly divided over the next steps.

While Democrats have the votes for a filibuster, Majority Leader Mitch McConnell is ready to lead the GOP in a unilateral change in a Senate floor procedure so significant that it has been dubbed the “nuclear option.” The tactic if invoked would lower the confirmation threshold to a filibuster-proof simple majority of 51 votes in the 100-member Senate rather than the 60 votes currently needed to stop delaying tactics by opponents.

The likelihood of more partisan wrangling left veteran GOP senators frustrated — and hoping that Democrats would relent in their opposition to the Colorado jurist.

The nuclear option would be “damaging to the Senate, damaging to them and damaging to the country. Maybe a light will come on somewhere,” said Sen. Lamar Alexander, a Tennessee Republican.

After hours of debate Monday, the Judiciary Committee voted 11-9, along party lines, to send Gorsuch’s nomination to the full Senate, where McConnell, R-Ky., has vowed he will be confirmed on Friday.

Sen. Chris Coons of Delaware became the key 41st vote for the Democrats, declaring during a committee debate that Gorsuch’s conservative record showed an activist approach to the law, often in favor of business interests, and that he evaded questions during his confirmation hearings. Coons also said that Republicans’ treatment of former President Barack Obama‘s Supreme Court nominee, Merrick Garland, left lasting scars after they denied him so much as a hearing following the death of Justice Antonin Scalia early last year.

“We are at a historic moment in the history of the United States Senate” due to actions by both parties, Coons said. “We have eroded the process for reaching agreement and dishonored our long traditions of acting above partisanship.”

The long-term consequences of the coming confrontation could be profound, as the rules change Republicans intend to enact would apply to future Supreme Court nominees as well, allowing them to be voted onto the court without any input from the minority party. And though predicting a justice’s votes can be difficult, confirmation of the 49-year-old Gorsuch is expected to restore the conservative majority that existed while Scalia was alive and that majority could be expanded in coming decades if Republicans remain in control of the process. Some of the more liberal justices are among the oldest on the court, so more court openings could pop up.

For Republicans and Trump, Gorsuch’s confirmation would be a moment of triumph, a bright spot in a troubled young administration that’s failed on the legislative front with the health care bill and is under investigation over Russia connections. The nomination of Gorsuch, by contrast, has won universal praise from Republicans, some of whom call his appointment Trump’s best move so far as president.

Gorsuch has spent more than a decade on the federal appeals bench in Denver where he’s issued consistently conservative rulings, and he appeared on Trump’s list of potential candidates partly generated by the Federalist Society and Heritage Foundation during the campaign.

Gorsuch’s confirmation would also serve as vindication for McConnell’s strategy of refusing to fill Scalia’s seat last year, instead leaving it open for the next president, even though few imagined then that that person would be Trump.

The showdown over the “nuclear option,” expected on the Senate floor Thursday, is likely to be accompanied by much hand-wringing from senators bemoaning the decay of the chamber’s traditions of bipartisanship and comity.

But both parties are to blame. When the Democrats were in the majority, they removed the 60-vote threshold for nominees to federal benches lower in the judicial system than the Supreme Court. This change came in 2013 as Republicans, who were in the minority at the time, were blocking Obama picks for critical court vacancies. Republicans said at the time that Democrats would come to regret the move.

Gorsuch will be confirmed “and he should be,” John Cornyn of Texas, the No. 2 Senate Republican, said during Monday’s debate. “If Judge Gorsuch is unacceptable to our Democratic colleagues, there will never be a nominee by this president that you will find acceptable. Never.”

Gorsuch now counts 55 supporters in the Senate: the 52 Republicans, along with three moderate Democrats from states Trump won last November — Joe Manchin of West Virginia, Heidi Heitkamp of North Dakota and Joe Donnelly of Indiana. A fourth Senate Democrat, Michael Bennet from Gorsuch’s home state of Colorado, has said he will not join in the filibuster against Gorsuch but has not said how he will vote on final passage.

Democrats claim the Republicans’ treatment of Garland was worse than anything they ever did or are doing, and with Trump in the White House they are under intense pressure from liberal voters to oppose the president on every front.