A Senate Democrat announced Monday that he will filibuster Donald Trump's nominee to the Supreme Court — setting up what would be only the second time in modern history that a nominee to the Court has been filibustered.

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"We will use every lever in our power to stop this," Oregon Sen. Jeff Merkley told Politico. "A very large number of my colleagues will be opposed."

In practical terms, a filibuster from Senate Democrats will almost certainly not prevent Trump from getting whichever nominee he wants. Even if all Senate Democrats decided to join Merkley, Majority Leader Mitch McConnell has enough Republican votes to do away with the filibuster for Supreme Court nominations — and then invoke cloture to cut off debate.

It's also still not clear how many Senate Democrats will be behind Merkley's effort. In an interview on Monday, Massachusetts Sen. Ed Markey said he was first waiting to see whom Trump puts forward before committing to a filibuster.

Still, Markey wouldn't take filibustering off the table either. "There's no question that if President Trump does not name a nominee who is in the mainstream ... that this will be a huge battle that I'll be a part of in trying to block," he said.

Supreme Court nominees emerge

Right now the leading contenders for the high court are Thomas Hardiman of the Third Circuit US Court of Appeals and Neil Gorsuch of the 10th Circuit Court of Appeals. (Vox's Dylan Matthews has a rundown of their previous positions here.)

In his interview with Politico, Merkley argued that Senate Democrats should not have to cooperate with Republicans given that the Republican Senate torpedoed President Obama's Supreme Court nominee, Merrick Garland. McConnell refused to schedule a hearing for Garland for nearly a year, effectively killing his chances at the bench.

But McConnell's spokesperson Don Stewart argued that that Senate Democrats were wrong to threaten a filibuster against Trump's nominee. In an interview, Stewart said that McConnell's opposition to Garland was not based on partisan opposition to an Obama nominee, but rather based on a desire to see the seat see filled after the presidential election.

"We said, 'We'll wait for the next presidency to fill the seat.' And we said that when people thought it was going to be Hillary Clinton," Stewart said. "It wasn't a situational thing. It wasn't, 'Oh, if a Republican wins, then we'll do it.' That's what Merkley's doing."

McConnell prevented Garland from getting a hearing in the Senate. His spokesperson argued that's different from what Merkley wants to do.

"McConnell has never filibustered a Supreme Court nominee," Stewart said.