The US Senate has voted to trigger the so-called "nuclear option" for confirmation votes on Supreme Court nominees.
The motion was passed along party lines - 52 Republicans voted for it, 48 Democrats voted against it.
President Donald Trump's nominee to fill the current Supreme Court vacancy, Neil Gorsuch, can now be confirmed by simple majority of 51 Senators, not the previously required 60.
With ideological control of the nation's highest court at stake, the Senate held a vote to end debate on Mr Gorsuch's nomination and move toward a Friday vote to confirm him to the lifetime post.
But with the 55-45 tally, Republicans fell short of the 60-vote super-majority needed to overcome the Democratic procedural tactic called a filibuster and proceed to a vote in which senators could confirm him by a simple majority.
Republicans immediately moved to vote on changing long-standing Senate rules in order to prohibit filibusters against Supreme Court nominees.
The rule change, which required a simple majority, was dubbed the "nuclear option" because it is considered an extreme break with Senate traditions, and Mr Trump has encouraged Mitch McConnell, the Republican leader in the upper house, to "go nuclear."
Republicans had said Mr Gorsuch would be confirmed on Friday one way or the other.
"This will be the first and last partisan filibuster of the Supreme Court," Mr McConnell said on the Senate floor ahead of the vote.
"In 20 or 30 or 40 years, we will sadly point to today as a turning point in the history of the Senate and the Supreme Court, a day when we irrevocably moved further away from the principles our founders intended for these institutions: principles of bipartisanship, moderation and consensus," Senate Democratic leader Chuck Schumer said on the Senate floor.
Senate confirmation of Mr Gorsuch, 49, would restore the nine-seat court's 5-4 conservative majority, enable Mr Trump to leave a lasting imprint on America's highest judicial body and fulfill a top campaign promise by the Republican president.
Republicans have called him superbly qualified for the job and one of the most distinguished appellate judges on the bench, and they blamed the Democrats for politicising the confirmation process.
Democrats accuse Mr Gorsuch of being so conservative as to be outside the judicial mainstream, favoring corporate interests over ordinary Americans in legal opinions, and displaying insufficient independence from Mr Trump.
"This isn't really about the nominee anyway," Mr McConnell said.
"The opposition to the this particular nominee is more about the man who nominated him and the party he represents than the nominee himself."
Democrats expressed anger that the Senate, under Mr McConnell's guidance, refused last year to consider Democratic former President Barack Obama's nomination of appellate judge Merrick Garland to fill the same high court vacancy that Mr Trump elected Mr Gorsuch to fill.
The Supreme Court has had a vacancy since conservative Justice Antonin Scalia died in February 2016.
"The nuclear option was used by Senator McConnell when he stopped Merrick Garland. What we face today is the fallout," Democratic Senator Richard Durbin said.
What Republicans did to Mr Obama's nominee was worse than a filibuster, Mr Schumer said.
He said Republicans denied "the constitutional prerogative of a president with 11 months left in his term."
Mr McConnell blamed the escalation of fights over judicial nominees on the Democrats and their opposition starting three decades ago to nominees made by Republican former presidents Ronald Reagan and George W Bush.
