WASHINGTON — A Democratic senator held the Senate floor through the night and was still going Wednesday in an attention-grabbing talk-a-thon highlighting his party’s opposition to President Donald Trump’s Supreme Court nominee, Neil Gorsuch.

But Senate Majority Leader Mitch McConnell claimed the votes necessary to change Senate rules and thwart the Democratic filibuster in a showdown that could alter the course of the Senate and the court.

Oregon Sen. Jeff Merkley started talking Tuesday evening and was still going more than 13 hours later as he accused Gorsuch of siding with corporations over regular people, likening Gorsuch’s approach to that of Antonin Scalia, the justice who died last year. Though Scalia died 14 months ago, Republicans held the seat open so President Donald Trump could fill it, sparking enduring Democratic fury.

Merkley stood in front of a blow-up of the preamble to the Constitution, still talking Wednesday morning.

He said Gorsuch “is much like his idol and role model Antonin Scalia and other far-right conservatives on the Supreme Court. And while this unbalanced approach might make for interesting reading the courtroom is not an academic paper each case involves real people with real problems.”

Merkley’s lengthy speech made for drama but had no chance to change the outcome. In votes set for Thursday, Democrats will try to block Gorsuch’s confirmation, but McConnell will then change Senate rules to lower the threshold required to advance Supreme Court nominees from 60 votes to a simple majority in the 100-member Senate.

“They seem determined to head into the abyss,” the Kentucky Republican said of Democrats as debate began Tuesday over Judge Neil Gorsuch’s nomination. “They need to reconsider.”

Democrats blamed Republicans for pushing them to attempt a nearly unheard of filibuster of a qualified Supreme Court pick. Forty-four Democrats intend to vote against proceeding to final confirmation on Gorsuch, which would be enough to block him under the Senate’s existing parliamentary rules that require 60 votes to advance a nomination.

But McConnell intends to act unilaterally with the rest of the 51 other members of the GOP Senate conference and change the rules to eliminate the 60-vote threshold so that it would require just a simple majority to install Gorsuch on the high court bench, as well as all future Supreme Court nominees. Asked if he has the votes to do that, given misgivings voiced by many Republicans, McConnell answered simply “yes.”

Democrats tried mightily to keep the focus on Republicans’ plans to change Senate rules, rather than on their own plans to obstruct a nominee who would likely have gotten onto the court easily with no filibuster in earlier, less contentious political times.

Senate Minority Leader Chuck Schumer of New York said, “Senator McConnell would have the world believe that his hands are tied. That the only option after Judge Gorsuch doesn’t earn 60 votes is to break the rules, to change the rules. That could not be further from the truth.”

In fact, a Senate rules change does appear to be the lone route that Republicans have to put Gorsuch on the court. And despite claims from Schumer and others that Trump and Republicans could go back to the drawing board and come up with a more “mainstream” nominee, it seems unlikely that any nominee produced by Trump would win Democrats’ approval.

On Tuesday evening McConnell officially filed a “cloture” motion, the procedural step designed to end debate on a nomination and bring it to a final vote. That started the clock toward a showdown on Thursday, when Democrats are expected to try to block Gorsuch, at which point Republicans would respond by enacting the rules change. The change is known on Capitol Hill as the “nuclear option” because of the potential repercussions for the Senate and the court.

For the Senate, it would mean that future Supreme Court nominees could get on the court without bipartisan support, potentially leading to a more ideologically polarized court. More immediately, Gorsuch’s confirmation to fill the vacancy on the court created by Scalia’s death would restore the conservative voting majority that existed before Scalia’s death and could persist or grow for years to come.

And for the Senate, lawmakers of both parties bemoaned the further erosion of their traditions of bipartisanship and consensus. Some were already predicting that they would end up eliminating the 60-vote requirement for legislation, as well as nominations. But McConnell pledged Tuesday that this would not happen on his watch.

Gorsuch now counts 55 supporters in the Senate: the 52 Republicans including McConnell, along with three moderate Democrats from states that President Donald Trump won last November — Joe Manchin of West Virginia, Heidi Heitkamp of North Dakota and Joe Donnelly of Indiana. A fourth Senate Democrat, Michael Bennet from Gorsuch’s home state of Colorado, has said he will not join in the filibuster against Gorsuch but has not said how he will vote on final passage.

Gorsuch, 49, is a 10-year veteran of a federal appeals court in Denver where he’s compiled a highly conservative record that’s led Democrats to complain that he too often sides with corporations without regard to the humanity of the plaintiffs before him.

Associated Press writer Mary Clare Jalonick contributed to this report.

Supreme Court Justice nominee Neil Gorsuch testifies March 21, 2017, on Capitol Hill in Washington during his confirmation hearing before the Senate Judiciary Committee. A divided Senate Judiciary Committee backed Gorsuch, Monday, April 3, 2017. GOP likely to change Senate rules to confirm him.Democratic members of the Senate Judiciary Committee, Sen. Chris Coons, D-Del., left, and Sen. Richard Blumenthal, D-Conn. confer on Capitol Hill in Washington, Monday, April 3, 2017, as the panel met to advance the nomination of President Donald Trump’s Supreme Court nominee Neil Gorsuch. Senate Judiciary Committee Chairman Sen. Charles Grassley, R-Iowa, wraps up the meeting on Capitol Hill in Washington, Monday, April 3, 2017, after his panel voted along party lines on the nomination of President Donald Trump’s Supreme Court nominee Neil Gorsuch.Senate Majority Leader Mitch McConnell of Ky. speaks to reporters on Capitol Hill in Washington, Tuesday, April 4, 2017, about the struggle to move Supreme Court nominee Neil Gorsuch toward a final up-or-down vote on the Senate floor.