WASHINGTON ― Democrats have locked in the votes to block Supreme Court nominee Neil Gorsuch, meaning Republicans will have to take the extreme step of using the so-called “nuclear option” to blow up Senate rules to confirm him.

Democratic senators have been vowing for weeks to deny a vote to President Donald Trump’s court pick, and have been inching closer to the 41 members they needed to filibuster him. They hit the magic number on Monday when Sen. Chris Coons (D-Del.) announced he will join the blockade.

“I will be voting against cloture,” Coons said, using technical terms to mean he will support the Democratic filibuster, “unless we are able, as a body, to finally sit down and find a way to avoid ‘the nuclear option’ and ensure that the process to fill the next vacancy on the Court is not a narrowly partisan process.”

Republicans now have a choice: cave to Democrats’ demands that Trump put forward a different nominee (highly unlikely) or unilaterally change the rules so they can confirm Gorsuch without Democrats (likely). They’re signaling they’re prepared to use the nuclear option, a rarely invoked procedural maneuver, to lower the threshold from 60 votes to 51 votes to advance a Supreme Court nominee. There are currently 52 Republicans, so the rule change would mean they could confirm Gorsuch on their own.

Bill Clark/CQ Roll Call Senate Minority Leader Chuck Schumer (D-N.Y.) succeeded in rounding up the votes to filibuster Supreme Court nominee Neil Gorsuch.

Nobody really likes the idea of changing that rule. There’s currently a filibuster rule in place for Supreme Court nominee and for bills (Democrats got rid of the rule for lower court nominees in 2013). If Republicans got rid of the 60-vote requirement for Gorsuch, some fear it’s only a matter of time until senators do away with the filibuster rule altogether. That would make the Senate function a lot more like the House, where simple majority rules, and erode the institution of the Senate, which prides itself on requiring consensus to get things done.

“It makes me very sad,” Sen. John McCain (R-Ariz.) said last week.

Partisan tensions are high. Democrats are still mad at Republicans for the way they treated President Barack Obama’s Supreme Court nominee, Merrick Garland. The GOP spent all last year refusing to even give Garland a hearing, and held over the vacant Supreme Court seat for Trump to fill with Gorsuch. Democrats are also under intense pressure from their base to stop Gorsuch. Republicans, meanwhile, are angry that Democrats are forcing them to decide between confirming Gorsuch and gutting Senate rules they actually like.

Gorsuch appears on track for his procedural vote, the “cloture” vote that Democrats plan to filibuster, on Thursday.