A new paper from Health Matrix: Journal of Law-Medicine suggests that a missing word in the Affordable Care Act, the 2000-page law which created Obamacare, may scupper a key provision of the plan.

The Act brings into existence health insurance exchanges, federally- and state-run institutions which centralise and regulate the process of buying health insurance for people with enough income to not be eligible for Medicare. It also lays out who can get federal subsidies to buy insurance from those exchanges, the idea being that those subsidies will gradually encourage people to migrate from America's current system of employer-provided insurance to a saner system of individuals buying their own healthcare, which will hopefully lead to, among other things, fewer people dying as a direct result of losing their job.

Unfortunately, the authors of the article alledge that a drafting error by the administration's lawyers has rendered that aim unachievable. In the passage laying out who can get that crucial federal subsidy, Article 1401 the law restricts eligibility to those who "enrolled … through an Exchange established by the State under 1311." And Article 1311 defines an exchange as a "governmental agency or nonprofit entity that is established by a state."

Crucially, the definition of an exchange, for the purposes of the federal subsidy, seems to exclude federal exchanges.

The authors argue that this is on purpose, citing the words of the head of the Senate finance committee that "the bill conditions the availability of tax credits on each state creating its own Exchange". The Obama administration obviously believes the latter, with the Washington Post's Sarah Kliff arguing that:

There’s another part of Section 1401 — Section 1401(f)(3), to be exact — that requires both federal and state exchanges to report information about any credits being administered. Why would federal exchanges need to report that information, the thinking goes, if they were not administering credits?

If the difference in phrasing is a genuine mistake - a so-called "Scrivener's error" - then it will lead to a mildly embarrassing court case where that point is clarified, and that's that. But if the administrations lawyers actually did miss a clause inserted by one of the co-authors which fundamentally changes the meaning of the law, this one could run and run.