WASHINGTON (Reuters) - The U.S. Senate moved on Tuesday toward ramming through approval of President Donald Trump’s Supreme Court nominee this week, as its top Republican said he had the votes to wipe away Democratic roadblocks but vowed to preserve the minority party’s ability to hold up legislation.

Majority Leader Mitch McConnell plans to change the Senate’s long-standing rules in order to eliminate the ability to use a procedural hurdle called a filibuster against Supreme Court nominees like Trump’s pick, Neil Gorsuch, if a Democratic filibuster succeeds as expected in blocking a confirmation vote.

Senate confirmation of Gorsuch, 49, to the lifetime post would restore the court’s conservative majority and enable Trump to leave a lasting imprint on America’s highest judicial body even as he regularly criticizes the federal judiciary.

McConnell said he had the necessary votes to approve the rule change with a simple majority vote, expected on Thursday. Republicans control the Senate 52-48. The rule change has been dubbed the “nuclear option,” and Trump has encouraged McConnell to “go nuclear.”

Such a step would threaten to further erode trust between the parties in Congress.

“There’s a reason they call it the nuclear option, and that is because there’s fallout. And this fallout will be dangerously and perhaps disastrously radioactive for the Senate for years to come,” Democratic Senator Richard Blumenthal told reporters.

Republicans were so confident they could use their muscle to pass the rule change that Senate Judiciary Committee Chairman Chuck Grassley said flatly that Gorsuch “will be on the Supreme Court Friday night.”

Amid a fierce debate over both Gorsuch and the Senate’s rules, McConnell tried to tamp down any speculation that Republicans would stage a monumental power grab by ending the filibuster for legislation.

McConnell said that as long as he was the Senate’s majority leader, he would never remove the ability to mount a filibuster against legislation, as opposed to presidential appointments. McConnell fought against many of former Democratic President Barack Obama’s legislative initiatives when Republicans were the minority party in the Senate.

Supreme Court nominee judge Neil Gorsuch testifies. REUTERS/Jonathan Ernst/File Photo

“There’s not a single senator in the (Republican) majority who thinks we ought to change the legislative filibuster, not one,” McConnell told reporters.

The move to change venerable Senate rules reflects an intensifying of the already-toxic partisanship in Washington since Trump took office in January.

McConnell’s promise to keep the ability to filibuster legislation could make it more difficult for Republicans to get key parts of Trump’s legislative agenda through the Senate, considering the expected strong Democratic opposition.

‘BREAK THE RULES’

A filibuster requires a super-majority of 60 votes in the 100-seat Senate in order to proceed to a simple majority vote on a Supreme Court nominee or legislation.

The 60-vote super-majority threshold that gives the minority party power to hold up the majority party has forced the Senate over the decades to try to achieve bipartisanship in legislation and presidential appointments.

The Senate on Tuesday kicked off its formal debate on confirming Gorsuch, a Colorado-based appeals court judge, and McConnell said he would get the clock ticking toward a vote expected on Thursday to stop the Democrats’ filibuster.

Democrats on Monday amassed the votes needed to sustain the filibuster, prompting Republicans to move toward changing the rules.

Democratic Senator Jeff Merkley took to the Senate floor on Tuesday evening to rally support for the Gorsuch filibuster. His office said in a statement that he “plans to hold the floor and refuse to yield for as long as he is able to continue speaking.” Merkley’s “talking filibuster” is not expected to affect the Republican timetable for Gorsuch’s confirmation.

The filibuster in one form or another dates back to the 19th century but assumed its current form in the 1970s.

The Democrats were the first to use the “nuclear option.” In 2013, when they controlled the Senate, they changed it to bar filibusters for executive branch nominees and federal judges aside from Supreme Court justices. They did so after Republicans filibustered Obama’s appeals court nominees.

“Democrats are now being pushed by far-left interest groups into doing something truly detrimental to this body and to our country,” McConnell said on the Senate floor. “They seem to be hurtling toward the abyss this time, and trying to take the Senate with them.”

Top Senate Democrat Chuck Schumer, leading the filibuster effort, said it was the Republicans who bore responsibility for the crisis and for deciding, as he said, to “break the rules.”

He noted that the Senate, under McConnell’s guidance, refused last year to consider Obama’s nomination of appellate judge Merrick Garland to fill the same high court vacancy that Trump elected Gorsuch to fill.

“What the majority leader did to Merrick Garland by denying him even a hearing and a vote is even worse than a filibuster,” Schumer said on the Senate floor.

Restoring the nine-seat high court’s conservative majority would fulfill one of Trump’s top promises during the 2016 presidential campaign.

Republicans say Gorsuch is well qualified for the job and that there is no principled reason to oppose him. Democrats say he is so conservative as to be outside the judicial mainstream, has favored corporate interests over ordinary Americans in legal opinions, and has shown insufficient independence from Trump.