The general explanation of the Obama administration’s controversial, precedent-setting recess appointments is that they were just another salvo in the ongoing war being waged between the White House and congressional Republicans over nominations. The less obvious, but perhaps more true, interpretation is that Wednesday’s appointments are a salvo in an ongoing war over a controversial tactic that congressional scholar Thomas Mann has dubbed “a modern-day form of nullification.”

Obama made four recess appointments Wednesday. One of them lifted Richard Cordray to head the Consumer Financial Protection Bureau. Another added three members to the National Labor Relations Board. But despite having hundreds of nominees waiting in the wings, Obama didn’t pull a Teddy Roosevelt and make 160 appointments on the same day. What makes these four nominees different from all other nominees?

The answer is that, without them, the institutions they’re intended to lead will fail. In the absence of a director, the CFPB can’t exercise its powers. The expiration of Craig Becker’s term on the NLRB, meanwhile, means the board is about to fall from three members to two members — a number that the Supreme Court has ruled is less than a legal quorum, and so a number that means the NLRB cannot make binding rulings.

This is not an accident: Republicans have straightforwardly argued that they would obstruct the confirmation of any and all nominees to the CFPB until the Obama administration agreed to radically reform the agency. They were, in other words, using their power to block nominations to kill or change agencies that they didn’t have the votes to reform through the normal legislative order. Much the same has been happening at the NLRB. That’s what Mann means when he invokes “nullification”: Just as the original nullification crisis was about states refusing to implement federal laws that their representatives did not have the votes to overturn, the modern-day incarnation features Republicans refusing to implement laws they don’t have the votes to overturn. And this is what Obama is fighting.

But that doesn’t explain why Obama is limiting his fight to agencies facing obstruction-induced obsolescence. The underlying legal theory allows recess appointments for any reason. And there are a lot of empty chairs around the federal government right now.

There are two empty seats on the Federal Reserve’s Board of Governors. There’s an acting director running the agency that oversees Fannie Mae and Freddie Mac who has foiled many of the administration’s more ambitious ideas to heal the housing market. There are acting directors atop the Federal Deposit Insurance Corp. and the Office of the Comptroller of the Currency. In a year when the Obama administration is unlikely to get much through Congress, these vacancies make it harder for the White House to do more through executive action, too. In some ways, then, the question isn’t why Obama is is making these controversial recess appointments, but why he’s limiting himself to appointing four of the 202 nominees languishing in the confirmation process.

Part of the answer is that it can be hard to persuade good candidates to accept recess appointments — particularly when the appointments are made under unusual, controversial circumstances, as is the case here. This is, frankly, somewhat difficult to believe: Is there really no qualified housing-policy expert in the nation who would be interested in spending two years overseeing Fannie Mae and Freddie Mac in a bid to better the worst housing market since the Great Depression? That seems unlikely. But to be fair, I’ve not actually tried to recruit any takers for the job.

Another piece is that bipartisanship matters more in some areas than others. Federal Reserve Chairman Ben S. Bernanke opposes recess appointments to the Federal Reserve Board, as the body has traditionally been nonpartisan and noncontroversial, and the Fed would like to keep it that way. Plus, administration officials hold out hope that their Noah’s Ark strategy — they have nominated one Republican and one Democrat — will lead to quick confirmations.

A third is that confirmed nominees are worth much more than recess appointees in certain positions. A recess appointee can stay only until the end of the next Senate term — in this case, the end of 2013. A traditionally confirmed appointee to the Federal Reserve’s board gets 14 years, and a judge gets a lifetime appointment.

There’s also an argument that the Obama administration can have it both ways. By aiming its recess appointments at institutions threatened with effective nullification, it simultaneously shows that it can overcome Republican obstruction but confines its new precedent to a narrow application. Perhaps, knowing that Obama can appoint who he wants if he so chooses, Senate Republicans will prefer a deal to a hundred recess appointments being made atop their objections.

But it seems at least as likely that Republicans retaliate by refusing to move any and all nominations. That leaves hundreds of unconfirmed nominees sitting in the cold. And, though the Obama administration might argue that it’s working under a narrow view of when you can and can’t make recess appointments over congressional objections, it is unlikely that the next Republican administration will resist the urge to follow the White House’s new precedent to its natural endpoint.