Democratic US Senator Jeff Merkley delivered one of the longer speeches in Senate history by holding the floor for more than 15 hours into Wednesday to oppose President Donald Trump's Supreme Court nominee.
Senate Republican leaders have scheduled a crucial procedural vote on the nomination of Neil Gorsuch for Thursday.
Most Democrats have pledged to block the conservative judge, and Merkley's show of stamina was a powerful if merely symbolic display of their opposition.
Republicans and Democrats have clashed bitterly over Gorsuch, with no signs that a damaging standoff will be averted.
Opposition Democrats insist they have the necessary votes to employ a blocking tactic known as a filibuster.
Sixty votes are needed to overcome a filibuster and end debate in the 100-seat Senate. Since Republicans hold 52 seats, they would need eight Democrats to break ranks and support Gorsuch.
Only four have done so to date.
The expected failure of the test vote sets the stage for Republican leaders to employ the "nuclear option," which would change Senate rules in order to advance the nomination -- and all subsequent Supreme Court nominees -- by simple majority vote.
A confirmation vote follows on Friday, after which Congress shutters for a two-week recess.
Democratic leaders employed the contentious nuclear option in 2013, frustrated by Republican obstruction of dozens of then-president Barack Obama's lower-court picks.
Democrats, who ran the Senate at the time, lowered the threshold for judge nominations to 51 from 60.
But they kept the three-fifths threshold in place for Supreme Court nominees.
Senate Majority Leader Mitch McConnell now stands to lower the bar for high-court nominees, too.
"I've been here through the night... to say how important this is to not do this," Merkley implored to a virtually empty chamber.
He noted that the Republican-led Senate failed to even hold confirmation hearings last year on Merrick Garland, Obama's pick to fill the seat, which opened when the conservative justice Antonin Scalia died in February 2016.
Now the vacant seat on the high court is being offered to Gorsuch, to the outrage of seething Democrats such as Merkley.
"The majority team in this chamber decided to steal a Supreme Court seat," the Oregon senator said during remarks that droned on into the early hours Wednesday.
"To fill this stolen seat will damage the court for decades to come."
Merkley's marathon came as evidence surfaced that Gorsuch appeared to have plagiarized some material for his 2006 book, "The Future of Assisted Suicide and Euthanasia."
Documents show that several passages read nearly verbatim to a 1984 article in the Indiana Law Journal, according to Politico.
The White House dismissed the charge as a "last-second smear," Politico reported.
Merkley's 15.5-hour speech was not technically a stand-up filibuster -- immortalized by Jimmy Stewart's character in the film "Mr Smith Goes to Washington" -- because it did not block Senate business.