Senate Majority Leader Mitch McConnell (R-KY) fired back at Minority Leader Chuck Schumer (D-NY) for his vow that Democrats will fight to keep the Supreme Court vacancy open if President-elect Donald Trump selects a nominee from out of the mainstream.

At a press conference Wednesday, McConnell mocked Schumer for expanding what Republicans labeled the “Biden rule'”– referring to a 1992 speech given by then Sen. Joe Biden (D-DE) discouraging the appointment of a Supreme Court nominee close to an election — while arguing that “the American people simply will not tolerate” Democratic efforts to obstruct Trump’s eventual nominee.

Last year, McConnell led a Republican blockade against even considering Merrick Garland, President Obama’s nominee to fill the late Justice Antonin Scalia’s seat, securing the vacancy for Trump.

“I noticed my counterpart Sen. Schumer announced yesterday that their goal was to apparently never fill the Supreme Court vacancy. That’s kind of an expansion of the Biden rule,” McConnell said, before reiterating his definition of the Biden rule.

(When GOPers cited the “rule” to block Garland last year, Democrats pointed out that Biden’s speech was about a hypothetical scenario and in the same speech he said he would be willing to consider a compromise moderate nominee.)

“Sen. Schumer said in the second Bush Administration he would not confirm the Supreme Court nominee in the last 18 months of President George Bush 43’s tenure. Apparently there is yet a new standard now, which is, to not confirm Supreme Court nominee at all,” McConnell said.

Tuesday evening, Schumer said on Rachel Maddow’s MSNBC show that Democrats are “not going to settle on a Supreme Court nominee.”

“If they don’t appoint someone who’s really good, we’re gonna oppose him tooth and nail,” Schumer told “They won’t have 60 votes to put in an out-of-the-mainstream nominee and then they’ll have to make a choice: change the rules.”

He added that it was hard for him “to imagine a nominee that Donald Trump would choose that would get Republican support that we could support” and when asked if he would do his best to hold the seat open, Schumer said, “absolutely.”

As a minority in the Senate, Democrats will not have much leverage in blocking Trump’s nominee, beyond filibustering the nominee in a floor vote. Republicans last year refused to even hold hearings on Garland — many declining to meet him in person, as is typically part of the process of a Supreme Court nomination — on the basis that the vacancy should be filled by Obama’s successor.