Washington — Judge Neil Gorsuch, President Donald Trump’s pick to serve on the U.S. Supreme Court, faced a critical blow on Thursday as Senate Minority Leader Charles Schumer, D-N.Y., said he would join with other Democrats in attempting to filibuster the nomination — a move that could complicate his confirmation and rewrite how the U.S. Senate conducts its business.

Since last year’s elections, Democrats have threatened to force Trump’s Supreme Court nominees to clear procedural hurdles requiring at least 60 senators to vote to end debate and proceed to a confirmation vote. Republicans are eager to confirm Gorsuch before an Easter recess, but with no Democrat expressing support for Gorsuch, they are threatening to change Senate rules to ensure the judge’s confirmation by allowing Supreme Court picks to be confirmed with a simple majority vote.

On Thursday, Schumer warned that they should focus instead on changing Trump’s nominee. “If this nominee cannot earn 60 votes — a bar met by each of President Obama’s nominees, and George Bush’s last two nominees — the answer isn’t to change the rules. It’s to change the nominee,” he said.

Among recent Supreme Court nominees, President Obama’s choices of Sonia Sotomayor and Elena Kagan each received more than 60 votes. Samuel Alito, chosen by President George W. Bush, was confirmed, 58-42, in 2006, but 72 senators voted to defeat a possible filibuster.

It is not clear that Democrats have the votes to block Gorsuch and to keep Republicans from changing the chamber’s way of doing business. But Schumer’s announcement is likely to further politicize a divided Congress. In the last 47 years of Supreme Court nominations — spanning the appointments of the 16 most recent justices — only Alito was forced to clear the 60-vote procedural hurdle to break a filibuster.

In a Senate speech, Schumer said that Gorsuch “was unable to sufficiently convince me that he’d be an independent check” on Trump. He said later that the judge is “not a neutral legal mind but someone with a deep-seated conservative ideology. He was groomed by the Federalist Society and has shown not one inch of difference between his views and theirs.”

The Federalist Society, a conservative legal group, was one of two organizations that provided a list of names to Trump to consider for his Supreme Court nomination.

Schumer’s opposition was widely expected, given his leadership of a party facing increased pressure to block all of Trump’s nominees and policy decisions. But his speech did not include calls for the rest of his chamber to join him in opposition — a sign that he is leaving political space for certain Democrats to find ways to work with Republicans, if necessary. Several Democrats are facing opposition from conservative organizations bankrolling a multimillion-dollar ad campaign designed to bolster Gorsuch.

In addition to Schumer, Sens. Thomas Carper, D-Del., and Robert Casey, D-Pa., also announced on Thursday that they would filibuster.