Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Senate GOP aims to confirm Trump court pick by Oct. 29: report Trump argues full Supreme Court needed to settle potential election disputes MORE (R-Ky.) on Thursday knocked Democrats over their ongoing debate about expanding the Supreme Court to appoint more liberal justices, an idea backed by a growing number of 2020 presidential candidates.

McConnell, speaking from the Senate floor, said adding seats to the high court is an "absurd notion" and accused Democrats of wanting to retaliate because they lost the 2016 White House race.

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"The idea that sometimes they lose elections and Republican presidents sometimes subsequently appoint Supreme Court justices is apparently no longer tolerated," McConnell said.

He added that the "far left" was trying "rewrite the rules" to "stack the court."

"So out of the ash heap of history came this talk of ‘court-packing.’ A notion that would threaten the rule of law and our American judicial system as we have long understood it. A radical proposal that has been dead and buried by bipartisan consensus for almost a century," McConnell added.

Once dismissed as a fringe idea, reforming the nation’s highest court is gaining traction with a growing number of Democratic 2020 candidates as progressive outside groups and high-profile officials, including former Attorney General Eric Holder Eric Himpton HolderThe Hill's Campaign Report: Trump's rally risk | Biden ramps up legal team | Biden hits Trump over climate policy Biden campaign forming 'special litigation' team ahead of possible voting battle Pompeo, Engel poised for battle in contempt proceedings MORE, have vaulted the idea into the national spotlight.

Supporters argue that it's necessary since Republicans and Trump have confirmed two Supreme Court justices and a historic number of influential circuit court judges after refusing to take up former President Obama’s final Supreme Court nomination in 2016. Republicans nixed the 60-vote filibuster for Supreme Court picks in 2017 and have moved appeals judges over the objections of home-state senators.

Sens. Elizabeth Warren Elizabeth WarrenHarris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda Judd Gregg: The Kamala threat — the Californiaization of America GOP set to release controversial Biden report MORE (D-Mass.) and Kamala Harris Kamala HarrisButtigieg stands in as Pence for Harris's debate practice First presidential debate to cover coronavirus, Supreme Court Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (D-Calif.) told Politico that the option should be on the table as part of a larger conversation among Democrats about the direction of the American judicial system. And Sen. Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (D-N.Y.) told "Pod Save America" that the idea was “interesting” and she would “need to think more about it.”

Republicans have seized on the fight as an example of Democrats shifting further to the left ahead of the 2020 election.

McConnell, on Thursday, urged Democratic senators to push back against talk of expanding the Supreme Court.

"I hope my colleagues will have the courage to look at these far-left agitators in the eye and tell them that some traditions and some institutions are more important than partisan point scoring," McConnell said. "I have to say at this point that kind of courageous statement would come as a pleasant surprise."