McConnell’s argument was theoretically based on a previous insistence from Democrats that Republican presidents not nominate a Supreme Court Justice if a vacancy arises during a presidential election year. Nicknamed “the Biden Rule,” then-Senator Joe Biden made that case during the George H. W. Bush presidency.
“Should a justice resign this summer and the president move to name a successor, actions that will occur just days before the Democratic Presidential Convention and weeks before the Republican Convention meets, a process that is already in doubt in the minds of many will become distrusted by all. Senate consideration of a nominee under these circumstances is not fair to the president, to the nominee, or to the Senate itself,” Biden argued at the time.
Chuck Schumer went even further in 2007 and called for a filibuster of hypothetical justices appointed by George W. Bush, who still had over a year left in his presidency. “We should not confirm any Bush nominee to the Supreme Court except in extraordinary circumstances,” Schumer said.