Trump Supreme Court pick Neil Gorsuch faces Senate showdown
Democrats have enough votes to use a tactic called a filibuster to thwart President Trump's Supreme Court nominee.
Four more Senate Democrats said they would use the procedural roadblock on the nomination of Neil Gorsuch, giving the party the 41 votes they need.
Republicans may then resort to the so-called "nuclear option", changing the rules to ram through their nominee.
The nomination went through committee on Monday.
The stage is now set for a showdown on Friday when it goes to the full Senate.
The standoff could leave Congress even more plagued by bitter gridlock.
Many Democrats say Mr Gorsuch has shown he is too prone to favouring corporations to earn their support.
Republicans control the Senate chamber by 52 to 48, but need 60 votes to overcome a Democratic filibuster.
But changing the rules means they can overcome the obstruction without 60 votes.
- What is a filibuster?
- Why is the US top court so important?
- Who are the current eight justices?
- Neil Gorsuch: Who is Trump's nominee?
Step towards doomsday? - Anthony Zurcher, BBC News, Washington
Depending on whom you ask, the US government on Monday will move one step closer to doomsday, or one step closer to preserving a conservative majority on the US Supreme Court.
The near certain approval of Judge Neil Gorsuch by the Senate Judiciary Committee on Monday sets up a high-stakes partisan showdown later in the week, when Senate Republicans will likely vote to confirm Mr Gorsuch, even if it means abandoning the long-held Senate filibuster rule.
Senate Democrats, prodded by the anti-Trump anger of their base, appear to have the votes to support a filibuster. Republicans, wary of a protracted battle with no obvious endgame, seem determined to confirm Mr Gorsuch with a simple majority - the so-called "nuclear option"
If this particular doomsday comes to pass, all that will be left of the once potent filibuster rule is a 40-vote Senate minority's ability to block major legislation - and there are some Republicans clamouring for a change there, as well.
The filibuster was considered a tool to promote bipartisanship in the Senate, allowing the minority to have input on lawmaking and judicial and executive branch staffing. In today's hyper-partisan environment, however, such sensibilities seem increasingly quaint.
The full Senate chamber is expected to vote on Friday after three days of debate.
At Monday's hearing, California Democrat Dianne Feinstein attacked the nominee's rulings in cases involving a sacked truck driver and an autistic child.
Mr Gorsuch sided with a haulage firm that sacked an Illinois driver after he left a trailer in 2009 when its brakes seized up in sub-zero temperatures and he began to feel numb from the cold.
Mrs Feinstein also railed against Mr Gorsuch's record as a lawyer in former President George W Bush's Justice Department on so-called "enhanced interrogation techniques".
But South Carolina Republican Lindsey Graham warned: "If we have to, we will change the rules. And it looks like we're going to have to."
Democrats are also still fuming at Senate Republicans for refusing to even consider then-Democratic President Barack Obama's Supreme Court nominee last year.
There has been a vacancy on America's highest court since conservative judge Antonin Scalia died in February 2016.
If confirmed, Judge Gorsuch would restore the conservative majority to the nine-seat bench, which holds the final say in US legal matters.