The Supreme Court oral arguments on the challenge by two businesses of the Affordable Care Act’s mandates on contraception coverage have gotten the most attention today, understandably so given the import of that case for future disputes pitting claims of religious freedom against duly legislated laws. But not far away, another court, the D.C. Circuit Court of Appeals, was hearing arguments in another case that, despite being generally viewed as a long-shot challenge, has the potential to have a far greater impact on the Affordable Care Act itself. If the contraception challenge succeeds, it just means that that one sliver of Obamacare is struck down. If this other challenge succeeds, both sides agree that it would blow up the entire law.

And given those stakes, it should cause the law’s supporters some disquiet that based on today’s arguments alone, two of the three judges on the panel—the two Republican appointees—appeared far more sympathetic to the arguments of the challengers.

As readers may recall from our previous coverage of this challenge, it revolves around an argument put forward in 2011 by Jonathan Adler, a law professor at Case Western University, and Michael Cannon, a health care analyst at the libertarian Cato Institute and a committed Obamacare foe. They argue that the law is being carried out in contravention with its text: The section decreeing that people will get federal subsidies to help them pay for private insurance plans says that the subsidies are available for those buying plans on new exchanges established by the states—and makes no explicit provision for subsidies for those buying plans in states where governors and state legislators left the creation of the exchange up to the federal government. The law’s challengers—represented in the D.C. Circuit case, Halbig vs. Sebelius, by lawyer Michael Carvin—say the limiting of subsidies to state-based exchanges was no mere drafting oversight but rather a deliberate attempt by Democrats who wrote the legislation to induce states to set up their own exchanges rather than rely on the federal government to do so.

The government and other defenders of the law counter that any confusion in the wording was inadvertent and that the rest of the law makes abundantly plain that the subsidies were intended to go to people buying plans in the exchanges regardless of whether they were established by the states or by the Department of Health and Human Services. They note that there is zero mention anywhere in the legislative history of the law’s drafting of the subsidies being used as an incentive for states to set up their own exchanges; if the subsidies were meant to be an inducement to the states, why weren't the law's authors and proponents actually, you know, advertising that inducement? And they point to other places in the law where it is plain that the subsidies were intended for people buying insurance on both state-run and federal-run exchanges, such as the requirement that both forms of exchanges report people’s insurance purchases to the Internal Revenue Service, which calculates the level of subsidy (technically a “refundable tax credit.”)

The stakes in the challenge are enormous—36 states have chosen not to set up their own exchanges, which means that if the courts side with the challengers, the millions of people who have bought coverage in those states (the vast majority of whom have receives subsidies to do so) would lose their subsidies and be left unable to afford coverage. This would in turn throw the individual insurance market into disarray as many of these people dropped their coverage—except, presumably, the sickest of people with the most incentive to keep it.