Mr. Trump and his Senate allies argue for extreme haste to ensure that a possible election loss does not affect their project to force a new ideological balance on the court. But it’s worse than that. The president himself has said he is counting on Judge Barrett’s hurried confirmation so that she can rule on what he appears to believe are the inevitable election disputes he will bring before the court. He has spoken in recent days about getting rid of “the ballots” and enlisting the court in stopping the Democrats’ voting “scam,” arguing that he needs a ninth justice of his choosing to ensure the court rules his way. Imagine the turmoil that would cause: A court hastily stacked with Trump nominees hands reelection to the president, based to a degree on his view that some Americans’ ballots should not count.

By acting with such supreme hypocrisy, Senate Republicans would substantially diminish not only their own tattered reputations but also the much more precious legitimacy of the court. Every time the justices handed down a conservative ruling, vast swaths of the country would not accept the result. And the anger will be tenfold greater if this new, packed court delivers the presidency to Mr. Trump under questionable circumstances.