The Republican party line — that it was an election year, so the American people should have a “voice” in the selection of the next justice — was a patent lie. The people spoke when they re-elected Mr. Obama in 2012, entrusting him to choose new members for the court. And the Senate has had no problem considering, and usually confirming, election-year nominees in the past.

Of course, Supreme Court appointments have always been political, and the court’s ideological center has shifted back and forth over time. But the Senate has given nominees full consideration and a vote even when the party in power has opposed a president’s choice. That is, until this year, when Republicans claimed that though the Constitution calls for the Senate’s “advice and consent,” senators aren’t obligated to do anything. This is a bad-faith reading of that clause, even if there is no clear way to force a vote. It certainly obliterates a well-established political norm that makes a functioning judicial branch possible. As Paul Krugman wrote in his column on Monday, institutions are not magically self-sustaining, and they “don’t protect against tyranny when powerful people start defying political norms.”

This particular norm is of paramount importance because the court’s institutional legitimacy depends on its perceived separation from the elected branches — a fragile concept in the best of times. By tying the latest appointment directly to the outcome of the election, Mr. McConnell and his allies took a torch to that idea — an outrageous gambit that, to nearly everyone’s shock, has paid off. But while Republicans may be celebrating now, the damage they have inflicted on the confirmation process, and on the court as an institution, may be irreversible.

The slope is both slippery and steep. If Republicans could justify an election-year blockade, what’s to stop Democrats in the future from doing the same? For that matter, why should the party controlling the Senate ever allow a president of the opposing party to choose a justice? Indeed, in the weeks before the election, Senate Republicans were threatening, with the encouragement of leading conservative thinkers, never to confirm anyone to fill the vacancy if Hillary Clinton won.

Can anything be done to repair the harm? One step — as obvious as it is unlikely — would be for Mr. Trump to renominate Mr. Garland. Conservatives will scoff, but they know he is as qualified for the job as anyone in the country. When Mr. Garland was floated as a possible choice for the Supreme Court in 2010, Orrin Hatch, the senior Republican senator from Utah, called him a “consensus nominee” and said there was “no question” that he would be confirmed with bipartisan support. That’s partly why Mr. Obama nominated him this time, and also why Mr. McConnell denied him a hearing — he knew he couldn’t prevent a Senate vote once Americans saw an eminently qualified and reasonable jurist testify on live TV.