The number of justices on the court, which is set by Congress, has fluctuated throughout the course of the nation’s history, reaching as many as 10 seats before settling on nine in 1869. In 2016, Sen. Ted Cruz suggested that if Hillary Clinton were elected, the Republican Senate should keep Justice Antonin Scalia’s seat empty, effectively bringing the number of justices down to eight.

Republicans currently hold six seats, while Democrats hold just three. Republicans were able to solidify control of the court under former President Donald Trump, after first refusing to advance Merrick Garland’s nomination under former President Barack Obama and then confirming Justice Neil Gorsuch after Trump’s election. Then after Justice Ruth Bader Ginsburg died last September, Republicans threw out the procedures they had previously embraced and confirmed Justice Amy Coney Barrett in a matter of weeks.

After Trump’s nomination of Coney Barrett, then-Senate Minority Leader Chuck Schumer faced pressure to stop her confirmation by any means necessary. When those myriad options fell short and Coney Barrett was pushed through, the conversation turned to expanding the court.

“Not only do these extremist judges threaten more than a century of progressive achievements,” read a letter to Schumer by 20 New York elected officials, “they threaten to foreclose the possibility of any future progress under a Democratic administration.”

But after Democrats lost races they hoped to win in Maine, North Carolina, and Iowa, some Democratic strategists argued that the talk of court packing and ending the filibuster had inspired more Republicans to vote, and discussion of the move was shelved.

In April, President Joe Biden created a commission to study possible reforms to the court, including adding seats. This past October, Biden promised to create such a commission if elected, saying the judicial system was “getting out of whack,” but said, “It’s not about court packing.”