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 to block the nominee.
Denver appeals court judge Neil Gorsuch is now set to be approved on Friday (US 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.
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 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 Republician senator John McCain.
"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 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.