In an open letter, a coalition of voting rights advocates has accused the Obama administration of breaking the law by failing to use the federal exchanges—those run through HealthCare.gov—to help people register to vote. I don’t think that’s right, but the letter nonetheless raises an important question: Even if it’s not legally mandated, why shouldn’t HealthCare.gov do more to register voters?

To reduce barriers to voting, the National Voter Registration Act of 1993 (NVRA)—also known as the “motor voter law”—requires DMVs in most states to facilitate voter registration. To reach the poor and disabled who don’t have driver’s licenses, “each State” must also designate certain “voter registration agencies” that will do the same thing. Those agencies must include “all offices in the State that provide public assistance.”

Because Medicaid counts as public assistance, and because you can register for Medicaid through the exchanges, all exchanges, both state and federal, would seem to qualify as voter registration agencies. Indeed, state-based exchanges are already treated as voter registration agencies. When you buy insurance on the California exchange, for example, you’re nudged to register to vote.

That’s not the case, however, if you buy health insurance through HealthCare.gov. In the administration’s judgment, the 34 federal exchanges are not voter registration agencies within the meaning of the NVRA—even though at first blush the statute seems to say they are. That has incensed the voting rights advocates, who believe that the Obama administration is flouting the law. They close their letter with a thinly veiled threat: “We hope to avoid litigation but we note that the NVRA contains a private right of action.”

Any such litigation isn’t likely to go anywhere. After defining in general terms what counts as a voter registration agency, the NVRA specifically says that such agencies may include “Federal and nongovernmental offices, with the agreement of such offices.” The statute also says that federal agencies, “shall, to the greatest extent practicable, cooperate with the States” in carrying out their responsibilities.

As the Second Circuit held in 2000, neither of these provisions makes sense if federal offices must automatically be treated as voter registration agencies. In the court’s words, “[i]f federal offices need not always cooperate with a State’s agency-based registration program, … it is hard to see how it can be said that the federal … offices in question must be designated as [voter registration agencies].”

The better interpretation is that federal offices don’t count as voter registration agencies unless the federal government consents. That’s the interpretation that makes best sense of the statute as a whole, a la King v. Burwell.

The voting rights advocates seem to acknowledge as much. They argue, however, that the federal exchanges ought to be treated as state agencies because they “are responsible for fulfilling all of the state’s obligations when operating an exchange.” But that’s a non sequitur. A federal office doesn’t cease to become a federal office when it performs state functions. It’s still a federal office. And nothing in the NVRA requires such offices to be automatically treated as voter registration agencies.

The administration is thus on sound legal footing in refusing to apply the NVRA to HealthCare.gov. At the same time, however, nothing is stopping the administration from designating the federal exchanges as voter registration agencies. Indeed, doing so would put HealthCare.gov on parity with the state exchanges and advance the purposes of the NVRA. Why not issue such a designation?

I’m speculating here, but I see three possibilities, none of them mutually exclusive. (To my knowledge, the administration hasn’t offered a public defense of its position.) First, the administration might worry about making Obamacare appear more political than it already is. Second, buying health insurance is hard enough. Why complicate the process unless strictly necessary?

Third, the NVRA technically puts the onus on the states to “designate” federal offices as voter registration agencies. But the 34 states with federal exchanges are mainly controlled by Republicans, and as a group they’re not exactly chomping at the bit to make voting easier. Most of those states would probably refuse to designate HealthCare.gov even if the administration consented to it.

I’m not sure I find these justifications compelling, either individually or collectively. Perhaps there are others that I’m overlooking. For now, however, it’s safe to say the Obama administration isn’t breaking the law—even though it could, and perhaps should, do more to encourage people to register to vote.