Republicans have taken the historic step of changing US Senate rules in order to ram through confirmation of President Trump's Supreme Court pick.
They invoked the "nuclear option" after Democrats used a tactic known as a filibuster for the first time in half a century to block the nominee.
Denver appeals court judge Neil Gorsuch is now set to be approved on Friday.
The move will leave Congress even more plagued by gridlock. Republican John McCain said: "Bad day for democracy."
At stake is ideological control of the nation's highest court, which has the final say on some of the most controversial US legal issues, from gun control to abortion to election financing to workers' and LGBT rights.
After falling five votes short on Thursday of the 60 needed to confirm Mr Gorsuch, Republican Senate leader Mitch McConnell retaliated by ordering a vote to rewrite the chamber's rules. It passed by 52-48 along party lines.
The legislative manoeuvre - called the nuclear option because it is so extreme - enables Mr Gorsuch to be approved by a simple majority in the 100-member Senate, where Republicans control 52 seats.
The fall of bipartisanship - Anthony Zurcher, BBC News, Washington
With the bang of a gavel, the nuclear option - that dramatic term for doing away with the ability of a minority of senators to block confirmation of a Supreme Court nominee - has been exercised.
Pundits and politicians may lament that Thursday's actions mark the end of comity and bipartisanship in the Senate. The reality, however, is that the Supreme Court nominee filibuster power was already dead and vigorous partisanship reigns supreme. This week just made it official.
That's why both sides long ago began apportioning blame for this move. Democrats point to the Republican Party's unprecedented decision last year to refuse to consider Barack Obama's court nominee, Merrick Garland. Republicans counter that the Democrats struck the mortal blow by abandoning the filibuster for lower court and executive nominees in 2013.
Given the sweeping power of the Supreme Court - it touches on every facet of American life - the stakes have become too high for little things like tradition and consensus-building to merit consideration.
Thursday was about the exercise of raw power. Republicans had the votes, and they wanted - they needed - their man on the high court to preserve their conservative majority. On Friday they will get him there.
The political nuke means that all future Supreme Court nominations can also be approved by simple majority, which lawmakers on both sides agree will erode minority-party rights in the Senate.
Senator Jeff Merkley, an Oregon Democrat, tweeted: "The dark deed is done. McConnell has just put a knife into the heart of our We the People republic."
Even top Republicans have misgivings about the move.
"I fear that someday we will regret what we are about to do. In fact, I am confident we will," said Mr McCain, an Arizona senator, as he entered the chamber on Thursday morning.
"It is imperative we have a functioning Senate where the rights of the minority are protected regardless of which party is in power at the time."
Democrats said they opposed Mr Gorsuch, 49, because they felt he had shown favour to corporations ahead of workers.
But they are also resentful that Republicans refused last year to even consider former President Barack Obama's choice for the high court.
Mr McConnell instead left open the seat to replace the late Supreme Court Justice Antonin Scalia in the hope of filling it with a conservative nominee after the election.
Democrats also used the "nuclear option" in 2013, when they removed filibusters against executive branch and judicial nominees for lower courts.
That followed what the Democrats complained was unprecedented obstruction by Republicans against Mr Obama's appointments.
However, they left the filibuster in place for Supreme Court nominees.