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 lead to a total revamp of 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 next month, but with no Democrat expressing support for Gorsuch, they are threatening to change Senate rules to ensure the judge's swift 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 Barack 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 an already 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 floor 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. One of the group's top leaders, Leonard Leo, is on leave from the organization as he advises Trump on the Supreme Court confirmation process and other picks to fill vacancies on the federal appeals courts.

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 Gorsuch. Both are up for reelection next year. Casey is one of 10 Democratic senators running next year from states that Trump won in the presidential election and who are being pushed by Republicans to work with them on the president's priorities.

The Judicial Crisis Network, which is spending at least $10 million on TV ads to convince Democratic senators, called Casey and other Democrats opposing Gorsuch "totally unreasonable" because "they will obstruct anyone who does not promise to rubber stamp their political agenda from the bench."

Senior Republicans have vowed that Gorsuch will be confirmed no matter what - a veiled threat to Democrats that they might use the so-called nuclear option to change the way senators confirm Supreme Court justices.

"If Judge Gorsuch can't achieve 60 votes in the Senate, could any judge appointed by a Republican president be approved with 60 or more votes in the Senate?" Senate Majority Leader Mitch McConnell, R-Ky., said this week.

In 2013, Democrats angered by GOP resistance to Obama's nominees changed the chamber's rules so that executive branch nominees and picks to serve on lower federal courts could be confirmed with simple majority votes. Supreme Court nominations were not included in the rules change.

Much of the Democratic resistance to Gorsuch centers on the GOP's decision last year to block consideration of Judge Merrick Garland, Obama's choice to replace the late Antonin Scalia.

But moderate Democrats being asked to support Gorsuch have said they are hoping that both parties can come to an agreement that leads to Gorsuch's confirmation and the preservation of current Senate traditions. Sen. Joe Manchin, D-W.Va., seen as the Democrat most likely to support Gorsuch, said he needed to hear more from the nominee but was warning Democrats not to filibuster if it meant risking the nuclear option.

"I'm gonna go talk to him. I haven't completely made up my mind. I'm gonna go talk to him next week, then I'll make my decision," he said. "But I just think the Senate is on a slippery slope."

Polls show more Americans support than oppose Gorsuch's nomination, though many have no opinion. Most recently, an NBC News/Wall Street Journal poll last month found 32 percent supporting Gorsuch, while 20 percent were opposed and nearly half said they don't know enough or have no opinion (48 percent). Gorsuch so far has earned less public support than past nominees.

But support for Democratic attempts to block Gorsuch varies. A Quinnipiac University survey last month found that 65 percent of registered voters believe Senate Democrats should allow a vote on Gorsuch's nomination; 25 percent said they should prevent such a vote. A CNN-ORC poll found 51 percent of adults believe Senate Democrats would be justified in blocking an up-or-down vote if "all or most of the Democrats in the Senate opposed Gorsuch's nomination."

After two days of answering senators' questions, Gorsuch was not present on Thursday as he was alternately praised for his independence and intelligence, and criticized as a threat to working people, the environment, children with disabilities and national security by those who testified before the committee. Throughout the day, nearly 30 people spanning the ideological spectrum testified before the committee on Gorsuch's record.

Judge John Kane, a fellow Colorado judge, assured the committee that Gorsuch knows that his social, political and religious views have no place on the bench.

"Gorsuch is not a monk, but neither is he a missionary or an ideologue," Kane said.

Human rights advocates raised concerns on Thursday about Gorsuch's tenure at the Justice Department during George W. Bush's presidency, when he worked on cases related to the detention of terrorism suspects. Gorsuch helped draft language designed to support Bush's claims of executive authority on matters of torture and the treatment of detainees.

Gorsuch told the committee this week that he was merely acting as an attorney for his then-client.

"Judge Gorsuch was closely involved in developing and defending these claims," Jameel Jaffer, head of the Knight First Amendment Institute at Columbia University, told the committee.

"It is not the case . . . that Judge Gorsuch happened to be a government lawyer at a time when the government - his client - endorsed torture and a sweeping view of presidential power. The government endorsed those things first, very publicly, and then Judge Gorsuch chose his client."

Whether Gorsuch would be willing to stand up to overreach by the president as the ninth justice, Jaffer said, is particularly important at a time when Trump has put in place an executive order banning travel to the United States by immigrants from six majority-Muslim counties and has said he would consider prosecuting U.S. citizens in the military commissions at Guantánamo.

The committee also heard a highly personal account directly from Jeff Perkins, the father of a child with autism whom Gorsuch ruled against in 2008. Perkins called the decision by the U.S. Court of Appeals for the 10th Circuit "devastating," requiring one parent to move to another school district to get his son, Luke, the education he needed.

"Judge Gorsuch felt that an education for my son that was even one small step above insignificant was acceptable," Perkins said.

Gorsuch's 2008 decision came under scrutiny on Wednesday after the Supreme Court unanimously ruled in another case that the standard Gorsuch applied for assessing the educational benefit for students with disabilities was too low.

Deanell Reece Tacha, a former 10th Circuit judge, defended Gorsuch's position in the 2008 case, saying he was following long-standing precedent in applying a standard that was also used by most other appellate courts. She called Gorsuch the "gold standard in public service."

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The Washington Post's Scott Clement and David Weigel contributed to this report.