A small number of Republican senators have expressed discomfort with this idea, but when was the last time public interest won out in today’s Republican Party?

The indefinite blockade not only hobbles the justices’ ability to resolve current cases, it takes open aim at the court’s legitimacy as the sole unelected branch of government. Because the court “has no influence over either the sword or the purse,” as Alexander Hamilton wrote in the Federalist Papers, its legitimacy and authority depend entirely on the shared public acceptance of its verdicts.

Today’s Republicans are essentially saying the court is nothing but another political body, and that justices should be treated as ideological sock puppets of the president who nominated them. Yes, the justices come with political beliefs and backgrounds, but that makes it all the more important to demand that they work harder than the rest of us to struggle against their biases and preserve their independence. This is why, for instance, Justice Ruth Bader Ginsburg was wrong to comment on Mr. Trump’s candidacy — words for which she later apologized.

Until this year, no one disputed that the president should have wide latitude in picking justices. In 1993, Senate Republicans voted overwhelmingly in favor of Justice Ginsburg, President Bill Clinton’s first nominee. And even though they voted in large numbers against Mr. Obama’s first two nominees, Sonia Sotomayor and Elena Kagan, they did not try to block those nominations from going forward. Senate Democrats voted unanimously to confirm Ronald Reagan’s choice of Justice Scalia in 1986 and allowed full votes on Robert Bork and Clarence Thomas, both of whom they strongly opposed.

In 2016, Republicans have blown this delicate balance to pieces, all to keep a conservative majority. Of course, the court has had a majority of Republican-appointed justices for nearly half a century, through the normal processes of advice and consent. But now, Republicans want to maintain that majority, even if that means tossing out all political norms. This majority, they hope, would promote a worldview where fewer people have rights, where women do not have reproductive choices, where lawmakers can make it harder for minorities to vote, where religious people are free to disregard laws protecting people they don’t like. Such a court could use a severe interpretation of the Constitution to ensure that American politics can be flooded with unlimited money, that reasonable gun restrictions are struck down, that corporate interests prevail over those of consumers, and that basic environmental regulations are turned back.

Make no mistake: That is the court Americans would get under a President Trump. Still, Senate Democrats would have an obligation to consider and vote on his nominees, just as Republicans would have that obligation to Mrs. Clinton’s choices. No doubt, there would be Democratic voices demanding that their senators mimic the Republicans’ shameful example. But the Constitution asks more of all of us than that. In the next Congress, regardless of who wins on Tuesday, the very survival of the court as an independent body will be at stake.