President Biden and Vice President Harris just endorsed term limits for the Supreme Court, but they are being vague about the details. Would the current justices have to abide by those limits or only future ones?

The silence is deliberate. A proposal that applied only to future justices would lose much of its appeal to Democrats. But any statute that limited terms for current justices would be blatantly unconstitutional.

The Constitution grants federal judges life tenure, subject only to impeachment if they fail to exhibit “good behavior.” Alexander Hamilton described it as “permanent tenure of judicial offices.” Progressives who hate the current conservative dominance of the Supreme Court think they have found a way around that provision. Congress would just create a new kind of judicial office. It would include the full powers of the Supreme Court, as we know them, for 18 years but more limited powers afterward.

Sen. Sheldon Whitehouse, a Rhode Island Democrat, and eight of his colleagues have sponsored legislation to create these offices. It says nothing about exempting the current justices. Presidents would nominate new justices every two years and, as they did so, the most senior justices would be demoted, no longer able to vote in the vast majority of cases. Justice Clarence Thomas would be the first to be affected by the new rules, followed by Chief Justice John G. Roberts Jr. and Justice Samuel A. Alito Jr.

But redefining the office doesn’t overcome the constitutional obstacle to term limits. Applying the bill to a sitting justice would mean, effectively, revoking his current office and appointing him to a new one. He would no longer have life tenure in the office to which a president had nominated him and the Senate had confirmed him.

Progressives who have gone along with the idea that Congress has the power to regulate the justices in this way should think about the implications. Republicans could win the presidential election and control of both houses of Congress this fall. Adam J. White, a conservative colleague of mine at the American Enterprise Institute who served on Biden’s commission on court reform, has already imagined how a ruthless Republican government could use the power that the Democrats’ constitutional theory offers them.

If a statute can remodel the justices’ offices, then Republicans would have the power to neuter the most recently appointed justice instead of the most senior one while appointing their own pick. It would be just as constitutionally faithful a move as the one Democrats are considering.

And then, of course, a future president and Congress could reshuffle the jobs again, restoring the powers of previously weakened justices and enfeebling a different set of them. Liberals could ultimately come out on top, or conservatives could, or the courts could stay in radical flux forever. Who knows? The effect on the rule of law and public confidence in it is easier to predict.

There are two fixes that might make the term-limit idea constitutional. One would be to apply the limit to sitting justices but do it via constitutional amendment instead of statute. The other would be to stick with a statutory change and exempt the current justices.

But where’s the fun in any of that for progressives? Calling for a constitutional amendment is almost always pure symbolism. Democrats are not going to get three-quarters of the states to agree to destroy the conservative majority on the Supreme Court. A statute that limits only future justices, meanwhile, is a kind of unilateral disarmament in the judicial wars. If a hypothetical President Harris worked with a Democratic Congress to adopt the idea, they would be making their own appointees less powerful than the current justices. That’s no way to bring Roe v. Wade back.