It’s been widely noted that one of the biggest challenges for the Obama administration in setting up the new federal exchange for health insurance was that the project was much bigger than anticipated. Why? Because far fewer states than expected decided to set up their own exchanges—36 of them left the task to the federal government. This meant the feds were left having to pull a huge web of databases, regulations and insurance offerings into healthcare.gov, and that the site was also hit with a greater rate of traffic than it would have been if more customers had gone to exchanges set up by their own states. Meanwhile, some of the states that did set up exchanges (though not all) have been faring far better.

Why did this happen? Why did so many states that fiercely guard their prerogative to handle their own affairs cede control of their health insurance markets to Washington?

Well, a disproportionate share of the credit or blame—depending on how you’re looking at it—goes to a person you’ve probably never heard of: Michael Cannon.

Cannon is a health care policy expert at the libertarian Cato Institute. He is engaging and sharp-witted. He is also an avowed opponent of the Affordable Care Act, and has for several years now been embarked on a legal crusade that, while a ways from triumphing, may have inadvertently played an outsized role in suppressing the number of states setting up their own exchanges, thereby greatly confounding the law’s implementation.

Cannon’s crusade, which has been joined by Case Western Reserve University law professor Jonathan Adler, is driven by the conviction that there is a debilitating hole in the law: as written, they argue, it provides subsidies to help people buy individual health insurance plans only in exchanges set up by the states, not by the federal government. Cannon maintains that this was deliberate, as an incentive to get the states to set up exchanges, and that the federal government is violating the law by offering subsidies on the federal exchange. Defenders of the law say this is hogwash, that the wording flaw he has identified is a semantic oversight, and that it was plainly understood at every step of the law’s drafting—to Democrats, Republicans, and budget analysts tallying the law’s costs—that the subsidies would be available on the federal exchange. After all, the exchange would collapse without subsidies to help lower and middle-income people afford coverage. For more, see my colleague Jonathan Cohn’s summary a year ago.