When Justice Antonin Scalia died in early 2016, liberals and conservatives alike agreed that the next justice could transform American life for a generation or more. Donald Trump warned that if Hillary Clinton got to make the appointment “our country is going to be Venezuela.” Mrs. Clinton responded that a Trump justice “would threaten the future of our planet.” The partisan forecasts are even more ominous as Senate hearings begin next week on Mr. Trump’s nomination of Brett Kavanaugh to succeed Anthony M. Kennedy on the Supreme Court.

A single judicial seat should not be so freighted. And it might not be, if the court weren’t so willing to insert itself in disputes that ought to be resolved by the political process. We’re a long way from the notion of judicial restraint described by Justice Louis Brandeis a century ago. “The most important thing we do,” he said, “is not doing.”

We may pride ourselves that we have self-government, but for decades we’ve turned to the court to settle our most difficult social and political issues: abortion and gay marriage, campaign finance and gun control, even a disputed presidential election. When the justices rule the way we like, we laud them for “interpreting” the Constitution. When they don’t, we complain they’re “making the law” based on their own predilections. A good justice is an umpire; a bad justice is a player. No real principle seems to be involved in our assessments of the court, only whether we endorse the outcome of this case or that one. The court has become just another political prize to be won by the party in power, not the neutral arbiter this country’s founders envisioned.

“We need more Republicans in 2018 and must ALWAYS hold the Supreme Court!” President Trump tweeted this past spring. That kind of cynicism corrodes any legitimacy the court has left.