A “nuclear” confrontation is brewing in the Senate over the nomination of Judge Neil Gorsuch to the Supreme Court — with Democrats threatening a historic filibuster, and Republicans pledging a historic rules change in return.

Republican leaders have warned that they would resort to a “nuclear option” to avert an impasse, changing Senate rules to require a simple majority to end debate on the nomination, rather than 60 votes. President Trump has endorsed the option, last month urging Majority Leader Mitch McConnell to “go nuclear” if needed.

But Minority Leader Chuck Schumer, announcing his opposition to Gorsuch from the Senate floor Thursday, warned Republicans against such a move. “If this nominee cannot earn 60 votes ... the answer isn’t to change the rules; it’s to change the nominee.”

There is a good chance that 60 senators would not vote to end debate in the current political climate, thus forcing the GOP’s hand on the nuclear option — although the matter is far from settled. Democrats’ vote counter, Sen. Dick Durbin, told CNN on Wednesday that Gorsuch is likely short of that threshold for now.

The escalation by Democrats comes as the Senate Judiciary Committee wrapped up its fourth day of confirmation hearings Thursday, including roughly 20 hours during which Gorsuch fielded questions from panel members. Gorsuch was disciplined in his responses, attempting not to tip his hand on how he might decide cases — but Democrats grew frustrated, with many insisting he did not reveal enough about his thinking.

“There’s been an almost seismic shift in the caucus [against Gorsuch]," Schumer told Politico on Thursday. "He did not win anybody over with his testimony.”

The threat of filibuster in the context of a Supreme Court nomination is a relatively recent phenomenon. Even Clarence Thomas did not face a filibuster, although his 1991 confirmation process drew unprecedented controversy, and he only narrowly won Senate approval. Democrats threatened to filibuster Samuel Alito’s nomination in 2006, but they fell short of the votes needed to do so.

This moment in American politics is unusually heated, however, with Democrats under pressure to oppose and obstruct Trump at every turn. The high court nomination also carries extra baggage, with Democrats still seething over Republicans’ decision to block President Obama’s nominee, Merrick Garland, following Antonin Scalia’s death last year.

But Republicans hold their own grudge in this case: a rules change spearheaded by then-Senate Majority Leader Harry Reid in 2013, which nixed filibusters for Cabinet nominees and lower-court judges.

Democrats “are in no position to ask for any sort of a deal on anything,” said Sen. Chuck Grassley, chairman of the Judiciary Committee, citing that change.

Even Sen. Lindsey Graham, one of the Republicans who has most stridently defended Senate filibuster rules, told RealClearPolitics that he would support the nuclear option to confirm Gorsuch.

“If they filibuster him, it means there’s nobody a Republican could pick that they could support. That means they’re telling Trump they don’t recognize him as president,” Graham said. “... I’m not going to play that game and let them use the traditions of the Senate when they choose to and grab power when they want to.”

Graham said a few Democratic senators have approached him, looking for an avenue to keep the current rules in place. “I’m still hopeful,” Graham said, that 60 votes will come together to move forward on Gorsuch’s nomination following expected approval of the nominee by the judiciary panel on April 3.

Such an outcome would require eight Democrats to break with their party leaders, a risky proposition for many. Among those in the spotlight as key swing votes will be Democrats hailing from states where Trump won, and who face re-election in 2018. Montana Sen. Jon Tester, who falls into that group, said he’d spend some time evaluating the nomination this weekend before deciding whether to support cloture and final confirmation for Gorsuch.

“Schumer’s got to do what Schumer’s got to do. It’s fine,” Tester said of the leader’s filibuster threat. “We’re going to do what we’ve got to do.”