ON MARCH 4th the Supreme Court will hear arguments in King v Burwell, a case that could gut the Affordable Care Act (ACA), Barack Obama’s signature health-care law. It is the third legal challenge to Obamacare in four years to reach America’s highest court. In 2012 Chief Justice John Roberts surprised almost everyone by siding with the court’s liberal justices to uphold the constitutionality of the “individual mandate”, which requires most Americans to carry a health insurance policy. In 2014 he voted with the conservatives to allow certain businesses a religious exemption from providing some forms of birth control to female employees. This time, the challenge to the ACA is semantic. The case revolves around four words in the mammoth 906-page law that could bring the whole thing down. The inadvertent Trojan Horse consists of a seemingly innocuous subclause regarding the provision of tax credits to low and middle-income Americans, who otherwise could not afford to buy health insurance. These benefits may be allocated, the law reads, to people buying policies through "exchanges"—that is, online marketplaces (which Mr Obama likened to shopping on Amazon)—“established by the state.” The trouble is this: only 16 states opted to set up their own insurance exchanges. The rest were established by the federal government. When the Internal Revenue Service drafted its rules, it provided the tax credits to people who bought health insurance on both state and federal exchanges. But based on a literal reading of the law, the challengers in King contend, anyone who uses a federal exchange to buy health-care should not qualify for a federal subsidy. “As statutory construction cases go,” their brief trumpets, “this one is extraordinarily straightforward.”

The government responds that the very point of the ACA is to provide affordable health care to “all” Americans, not just to those who happen to live in states that established their own exchanges. Without these tax credits, around 7m Americans would suddenly find the cost of their policies rising to over 8% of their annual income, the threshold at which the ACA deems policies unaffordable. They would then be exempt from the individual mandate, shrinking the pool of subscribers and bringing on a so-called “death spiral” where insurance companies would be forced to increase premiums to stay solvent. Health care then becomes less accessible and more expensive for everybody. The government argues that the ACA’s challengers are essentially wrenching four words out of context to thwart the core mission of Obamacare.

The law may be ambiguous enough to merit so-called Chevron deference, under which courts defer to an agency's interpretation of a statute (and so the IRS would be given the benefit of the doubt). This was the basis of the Fourth Circuit panel's pro-ACA ruling now under review by the Supremes. But neither the petitioners nor the government spends much time on the Chevron matter in their briefs. Instead, both sides present their view of the law as clearly and unambiguously correct.

Both sides are half-right: the law says one thing in the troubled clause and means another more broadly. There seems to be no plausible way to read “established by the state” as meaning “established by the state or the federal government”. The petitioner’s brief hammers away at the grammar relentlessly, and effectively. As Linda Greenhouse of the New York Timesconceded in her expression of shock last autumn over the justices’ decision to hear King, “several sections of the Affordable Care Act...admittedly fit awkwardly together.” But on the other hand, there is no plausible reading of the ACA according to which the health-care law is specifically designed to destroy itself. The challengers may have a clear sense of what those four words mean out of context, but they are blind to the meaning of the law as a whole.

Implicitly appreciating the strength of the other side’s claims, both briefs try valiantly, but rather feebly, to invade the other’s turf. In its brief, the government takes pains to point to other language in the ACA to contend that “established by the state” is a “statutory term of art” embracing all of the exchanges, not only those set up by states. They argue, for example, that when the law assigns the Department of Health and Human Services as a fallback to “establish and operate such exchange within the state” if the state does not do so itself, it implies that a federally established exchange “is the ‘required exchange’ referenced earlier in the same sentence.” The brief even quotes the Black Law Dictionary definition of “such” as “those...having just been mentioned.” The grammatical parsing is heroic, if not quite fully persuasive.

The challengers are more disingenuous. In defending their position from the obvious charge that it subverts the core mission of the ACA, they lamely insist that their view of the law does not render “any other provision of the Act absurd.” But the ACA does begin to look like a ridiculously inefficacious lump under the challengers' understanding of the law. (The government’s brief uses bullet points to patiently explain how specific provisions would go limp if the court ends up restricting which users merit tax subsidies.) The challengers somehow insist that legislative purpose is beside the point. “Legislative history,” the brief reads, “is irrelevant.” At the same time, the challengers feel compelled to concoct a theory for why Congress would have inserted such a strange provision into the ACA in the first place. “[W]hat history does exist,” the petitioner argues, “shows that using subsidies to induce state action was consciously adopted by the Senate and clearly understood by ACA architects.” In other words, Congress deliberately denied tax benefits to people buying insurance through federal exchanges because it wanted to encourage the states to set up exchanges themselves.

But the idea that lawmakers meant to limit subsidies to buyers of health care on state exchanges appears to be false. An amicus brief submitted by “members of Congress who are current and former leaders of the committees that crafted the ACA” as well as “members of state legislatures who served during the period when their governments were deciding whether to create their own exchanges under the ACA” belies the petitioners’ speculation:

This objective, [Petitioners] claim, was so important that Congress drafted the ACA in a way that would guarantee the collapse of non-state-run Exchanges, even though that would drastically curb, rather than broaden, access to health insurance. Amici submit this brief to demonstrate that the purpose attributed to the statute by Petitioners was, in fact, never contemplated by the legislators who enacted the law, nor by the state officials charged with deciding whether to establish their own Exchanges. (emphasis added)

We still have the puzzle: why did Congress choose to use the phrase “established by the state”, if not to limit subsidies to policies bought on state exchanges? Members of Congress (who seem to be in a position to know) expose the petitioners’ hypothesis as specious, but the government’s contention that the phrase was selected as a “term of art” is rather precious. When the government says that its interpretation of the ACA “allows the Act to function as a ‘symmetrical and coherent regulatory scheme,’ with no need to rewrite, explain away, or ignore any of its provisions,” it seems to be lending the text of Obamacare an each-word-is-holy internal logic that it cannot quite bear. As Abbe Gluck, a law professor at Yale, has argued, the ACA is hardly an airtight tome. It is, in her view, “a very badly drafted statute”:

And it’s badly drafted for a simple reason that turns out to be important to understanding how the pending litigation should be resolved: Because Senator Ted Kennedy died in the middle of the legislative process and was replaced by Republican Scott Brown, the statute never went through the usual legislative process, including the usual legislative clean-up process.

But though “the statute is sloppy," Ms Gluck writes, "I think its meaning is plain.” This, in the end, is what King v Burwell comes down to: the Supreme Court will decide whether to let millions of Americans pay the price for their legislators' shoddy draftsmanship.