SENATE REPUBLICANS on Monday are likely to take a vote that is unfair, unwise and bad for the functioning of the government. Again.

For the third time in three weeks, the Senate will consider a presidential nominee to the powerful U.S. Court of Appeals for the District of Columbia Circuit. The first two nominees, Patricia Millett and Cornelia Pillard, failed to attract the 60 votes necessary to clear GOP filibusters. There’s little reason to think that dynamic will change for the third, Judge Robert Wilkins.

Senate Republicans are not assessing these nominees on their merits, as each deserves. Rather, Republicans have made them victims of a toxic and unresolvable “debate” about the proper size of the D.C. Circuit. Republicans accuse President Obama of attempting to tilt its ideological balance, which, of course, he is. And they argue that the court isn’t busy enough to require its vacant seats to be filled. Democrats insist the court still needs more active judges, and they point out that Republicans attempted to fill the court during the George W. Bush years, when the caseload wasn’t much different.

But the question of whether the D.C. Circuit needs all 11 of its judicial slots doesn’t need to be resolved to offer the president’s legitimate nominees a fair up-or-down vote, and Republicans are wrong to use that as a pretext to block them. It’s transparently self-serving of GOP lawmakers to oppose D.C. Circuit nominees only when it’s a Democrat’s turn to pick them. If Republicans truly are concerned that the court is too large, they should offer a plan to reduce its size — in future presidencies. That would separate raw partisan motivation from authentic concern about the state of the court system, and it’s the only sensible way to make changes to its size amid sharp partisan contention. In the meantime, Republicans should give the president’s legitimate, well-qualified nominees a fair hearing, instead of degrading further the already-broken process of staffing the government and the courts.

If the “debate” about the D.C. Circuit’s size should doesn’t end that way, Democrats might end it in another. Some of them would like to unblock the road for the president’s nominees by forcing rules changes that would limit the filibuster. Following the rejection of the two women and Mr. Wilkins, who is African American, even some fairly even-keeled senators might be inclined to agree. That’s a perilous path for the chamber that both sides probably would regret taking.

Instead, adults in the GOP should finally get together with Democrats and hammer out an understanding — the way previous judicial nomination crises have been resolved.