WASHINGTON (Reuters) - Senate Democrats are gearing up for a potentially ugly fight over Donald Trump’s U.S. Supreme Court pick, with some liberal activists urging them to do everything possible to block any nominee from the Republican president-elect.

A general view of the U.S. Supreme Court building in Washington, U.S., November 15, 2016. REUTERS/Carlos Barria

Democrats are still seething over the Republican-led Senate’s decision last year to refuse to consider outgoing President Barack Obama’s nomination of appeals court judge Merrick Garland for a lifetime post on the court. The action had little precedent in U.S. history and prompted some Democrats to accuse Republicans of stealing a Supreme Court seat.

Trump last week vowed to announce his appointment within about two weeks of taking office on Friday. He said he would pick from among 20 candidates suggested by conservative legal groups to fill the lingering vacancy caused by the death of conservative Justice Antonin Scalia last Feb. 13.

Scalia’s replacement could tilt the ideological leaning of the court for years to come, restoring the long-standing conservative majority that disappeared with Scalia’s death just at a time when it appeared liberals would get an upper hand on the bench.

Liberal groups are gearing up for a battle, with the People For the American Way calling the judges on Trump’s list of candidates “very extreme.”

“We’re hearing from Senate Democrats and parallel concern among outside groups that this is going to be a major fight,” said Marge Baker, the group’s executive vice president. “We’ll be arguing that Democrats use every means at their disposal to defeat the nominee. This is going to be ‘all hands on deck,’ using all means at our disposal.”

Senate Democratic leader Chuck Schumer has said it is hard for him to imagine Trump picking a nominee who Democrats could support, and said he would “absolutely” fight to keep the seat vacant rather than let the Senate confirm a Trump nominee deemed to be outside the mainstream.

“We are not going to make it easy for them to pick a Supreme Court justice,” Schumer told MSNBC on Jan. 3, adding that if the Republicans “don’t appoint someone who’s really good, we’re going to oppose them tooth and nail.”

Senate Democrats may be in a position to hold up Trump’s selection indefinitely. Senate rules require 60 votes in the 100-seat chamber to overcome a procedural hurdle called a filibuster on Supreme Court nominees. There are 52 Republican senators.

Assuming all 52 back Trump’s nominee, Senate Majority Leader Mitch McConnell either would need to lure eight Democrats to his side or change the rules and ban the filibuster for Supreme Court nominations. Republicans, then in the minority, complained that their rights had been trampled when Senate Democrats in 2013 voted to eliminate the filibuster for executive branch and judicial nominees beyond the Supreme Court.

‘THIS IS A FIGHT’

Baker said liberals cannot hold their fire for fear that Republicans will use this so-called nuclear option, adding, “At some point you don’t game this out. You say, ‘This is a fight.’”

Other liberal groups urged a more conciliatory approach.

“We’re not predisposed to opposition here,” said Kristen Clarke, president of the Lawyers’ Committee for Civil Rights Under Law.

Any nominee will be evaluated, Clarke said, adding that the group is girding for a nominee who is hostile to civil rights.

Trump’s nominee could influence the court on a wide range of issues including abortion, the death penalty, religious rights, presidential powers, gay and transgender rights, federal regulations and others.

Political considerations also hang over the confirmation fight. Democrats and the two independents aligned with them in the Senate will be defending 25 seats in the 2018 elections, while Republicans defend only eight.

Many of those Democratic seats are in Republican-leaning states Trump won in the Nov. 8 election, including West Virginia, Missouri, North Dakota, Indiana, Montana, Michigan and Ohio.

Republicans likely will target these and other Democrats in hopes of coaxing them into backing Trump’s nominee. That means Democratic senators such as West Virginia’s Joe Manchin, Indiana’s Joe Donnelly and Missouri’s Claire McCaskill could face extra pressure not to block Trump’s Supreme Court nominee.

The liberal groups are facing off with well-funded conservative adversaries. The Judicial Crisis Network, for instance, has said it will spend at least $10 million on advertising and grassroots efforts to pressure Senate Democrats to back Trump’s nominee.

Carrie Severino, the group’s chief counsel, said it would be hypocritical for Democrats to block a vote after arguing the Constitution required the Senate to act on Garland.

“A lot of them (Democrats) spent the last nine months saying there is a constitutional duty to have a vote. I’d find it shocking if they would not carry out what they think their duty is,” Severino said.

Nan Aron, president of the liberal Alliance for Justice, said the high level of interest the vacancy has generated among activists, lawyers, students and others makes up for the deep pockets of the other side. “I don’t think we’ll need $10 million given the outcry expressed already,” Aron said.