THE SENATE just unanimously confirmed President Obama’s latest nominee to the second-most powerful court in the country — the U.S. Court of Appeals for the District of Columbia Circuit. But don’t take that as a sign that the battle of the bench has abated. In fact, it’s about to get much bigger.

There are still three vacancies on the D.C. Circuit, and the New York Times reported on Monday that Mr. Obama wants to nominate three people at once to fill them — perhaps soon. That would alter the ideological composition of the court.

Republicans can’t argue with the fact that there are open slots or that Mr. Obama has the authority to appoint people to them. But they are poised to argue that the D.C. Circuit’s workload isn’t heavy enough to require new judges and that the president is trying to “pack” the court. Senate Republicans should be very familiar with this line; Democrats used a version of it to oppose a qualified George W. Bush nominee to the D.C. Circuit in 2006.

Partisan interests change; the principles that must guide the Senate in considering presidential nominees do not. For the government to function properly, the president must place nominees in open seats following a quick and fair review in the Senate. Fair does not mean opposing nominees because the other party disagrees with things would-be judges have written or said. Fair is not blocking appointments because they might change the ideological balance or because lawmakers view — for now — a court to be too big. The test is whether the president’s nominees to fill legitimate vacancies are well-qualified to serve. Both parties have violated these principles in recent years. But now it’s the Republicans who are in opposition.

Sure, it would take a little chutzpah for Mr. Obama to nominate three D.C. Circuit judges at once. The move dares Republicans to filibuster confirmation of the appointments or to turn tail. It would also cheer liberals who want to flip the conservative tilt of the D.C. Circuit, not merely to see well-qualified judges serve.

But it would take gall for Republicans to filibuster qualified nominees to bona fide openings on the D.C. Circuit on the grounds that Mr. Obama is trying to pack the court. That logic could be used to criticize any nomination that might upset the ideological disposition of an appeals bench. The president doesn’t just get to appoint judges to vacancies when the stakes are low.

Republicans had no objection to the size of the court when they voted to confirm Mr. Bush’s nominees not so long ago. Now they have flipped for the sake of pure partisanship. We have enough of that in Washington already.