West Virginia senator Joe Manchin said he won't block President Donald Trump's choice to replace Antonin Scalia on the Supreme Court, who is scheduled to be announced Tuesday evening.

"I'm not going to filibuster anybody," Manchin told THE WEEKLY STANDARD as he was heading into a luncheon Tuesday surrounded by reporters.

One of Manchin's Democratic counterparts, Oregon's Jeff Merkley, vowed Monday that enough Democrats would oppose the nominee to keep the individual short of the 60-vote threshold necessary to end debate and advance the process to a straight up-or-down confirmation vote. In 2013, former Majority Leader Harry Reid and his caucus invoked the "nuclear option" to allow a simple majority to end a debate on most nominations, but the change excluded Supreme Court picks. Those individuals are still subject to the 60-vote requirement (or three-fifths of the chamber, if there are missing senators).

Republicans control the Senate by a 52-48 margin, meaning seven other Democrats would need to join Manchin to end a filibuster. White House press secretary Sean Spicer tamped down concerns about such a scenario Tuesday, because "I think we're going to get the … senators, regardless, and I wouldn't be surprised if we get more."

But Democrats are stirring for a showdown. Senate minority leader Chuck Schumer has said his party would fight to block any nominee "out of the mainstream," a description some on the left are sure to attach to Trump's selection no matter who it is. The two leading contenders have strong bona fides on the right: a conservative lawyer told Jonathan Last in November that appellate Judges Neil Gorsuch and Thomas Hardiman are "certain constituonalists with testable records."

Merkley called the seat one of those two men appear set to fill "stolen", given the Senate's inaction last year on President Obama's nominee to succeed Scalia, Merrick Garland.

"We will use every lever in our power to stop this," he told Politico.

Were Democrats to filibuster the Supreme Court selection, Trump said he would encourage Senate majority leader Mitch McConnell to use the nuclear option. "I would. We have obstructionists," he told Fox News last week.

Before the election, Harry Reid said if Democrats won the Senate and White House, they would scrap the 60-vote hurdle for Supreme Court nominees if necessary. It remains unclear if Senate Republicans would do the same if 41 senators vote to block Trump's nominee.