The top Democrat in the Senate is warning President-elect Donald Trump about his eventual Supreme Court choice: Name a “mainstream” nominee or Democrats will oppose the individual “with everything we have.”

“My worry is, with the hard right running the show, that the likelihood of the nominee being mainstream is decreasing every day,” Sen. Chuck Schumer said Wednesday.

Asked to define mainstream, Schumer said, “You know it when you see it.”

Schumer’s comments foreshadow the fierce political fight over Trump’s choice for a lifetime job on a court whose rulings have the most far-reaching implications. The president-elect has said he wants to appoint a nominee to help overturn Roe v. Wade, the landmark 1973 decision that legalized abortion.

The New York Democrat made the comments a day after saying on MSNBC’s “The Rachel Maddow Show” that Democrats will “absolutely” do their best to keep the Supreme Court seat open if Trump doesn’t nominate someone whom Democrats could support.

The seat has been vacant for 11 months since the death of Justice Antonin Scalia last February. Senate Majority Leader Mitch McConnell, R-Ky., blocked consideration of President Barack Obama’s nominee, Judge Merrick Garland, saying the next president should make the pick. The strategy paid off, and the Republican Senate will consider whomever Trump nominates.

With the prospect of a Republican president making the choice, McConnell pushed back on Schumer’s comments about leaving the seat vacant.

“Apparently there’s yet a new standard now, which is to not confirm a Supreme Court nominee at all,” McConnell told reporters. “I think that’s something the American people simply will not tolerate.”

As minority leader, Schumer won’t have the same power as McConnell to block a nominee. But his words signal that Democrats could filibuster and force Republicans to round up 60 votes to move ahead. That will be a challenge for the GOP since they only hold 52 seats.

If Republicans can’t get enough Democratic votes, then they do have another option — change the rules and curb the filibuster for Supreme Court nominees. Former Senate Majority Leader Harry Reid, D-Nev., did that for lower court nominees and other nominations in 2013.

Schumer said on Maddow’s show that Garland, Obama’s unsuccessful pick, was “a very moderate, mainstream nominee.” Garland has been considered a liberal-leaning moderate in his years on the U.S. Court of Appeals for the District of Columbia Circuit.

Democrats have spent much of the last year criticizing Republicans for blocking Garland, insisting there should be a full slate of nine judges on the court. Republicans declined to even hold hearings on Garland’s nomination.

Schumer said his comments are “absolutely not” referring to the same type of obstruction tactics that Democrats blamed Republicans for in the last year.

“We have said that we will oppose nominees who are out of the mainstream, plain and simple,” he said. “We haven’t talked about hearings, we haven’t talked about any of these other issues.”

Schumer said he hadn’t yet reviewed a list of potential nominees that Trump circulated during the campaign, and said he wouldn’t comment on specific names.

In response to Schumer’s comments, Senate Judiciary Committee Chairman Charles Grassley, R-Iowa, said he thinks it’s “all the more important” that Trump choose someone who has been previously confirmed by the Senate by a decent margin. He indicated he believes federal court of appeals judges — like Garland — will be among those who will be strongly considered.

“I think both opponents and proponents of filling the vacancy are going to want it filled as fast as they can,” Grassley told Iowa reporters.

(AP)