THURSDAY'S RULING by a federal judge in Michigan upholding the constitutionality of the individual mandate to buy health insurance was just the first word on a subject almost certain to end up at the Supreme Court. The ruling came in a lawsuit filed by the Thomas More Law Center, a conservative public interest group that claimed that Congress overstepped its authority by requiring individuals, beginning in 2014, to obtain health coverage or pay a fine. U.S. District Judge George Steeh found that Congress acted consistent with its power under the commerce clause, which allows it to regulate interstate commerce.

The commerce clause question is a novel, and admittedly difficult, one. Over the years, the court has found that the clause gives Congress a wide berth in legislating, even in cases where the link to commerce, or to interstate activity, is rather hazy. "The Supreme Court has expanded the reach of the Commerce Clause," Judge Steeh noted, "to reach purely local, non-commercial activity, simply because it is an integral part of a broader statutory scheme." Thus, in the 1942 case of Wickard v. Filburn, the Supreme Court upheld a penalty imposed on a farmer for wheat grown purely for home consumption. In 2005, in Gonzales v. Raich, the justices said that Congress could prohibit the growing of marijuana solely for personal consumption. Still, as the plaintiffs in the health insurance case noted, the commerce clause has never been construed to regulate a choice not to purchase something.

The argument that congressional power stretches this far is that requiring uninsured individuals to obtain health insurance is central to the legislation's broader effort to keep costs under control. If obtaining insurance is optional, the uninsured who go to emergency rooms or require expensive care will end up shifting the costs of that uncompensated care onto doctors, hospitals and, eventually, in the form of higher rates, individuals who obtain insurance. Absent the individual mandate, the other aspects of the health-care legislation -- the requirement to extend coverage to individuals with preexisting conditions, for example -- would be unaffordable.

As Judge Steeh analyzed the case, the plaintiffs' decision was not whether to participate in the health-care market; everyone eventually does. Rather, he said, "as inseparable and integral members of the health care services market, plaintiffs have made a choice regarding the method of payment for the services they expect to receive. The government makes the apropos analogy of paying by credit card rather than by check."

The implications of individual choices on paying for health care have at least as great an effect on the broader economy as Roscoe Filburn's decision about how much wheat to plant. We think the capacious contours of the commerce clause, as interpreted by the Supreme Court for decades, support the imposition of the individual mandate. But we think that is a closer call, and more of an extension of existing doctrine, than Judge Steeh's ruling acknowledges. Whether to buy insurance or handle health-care costs another way is a bigger difference than credit card or check. We were glad to see the mandate upheld but look forward to hearing from more courts on the underlying theory -- and what limits it imposes on federal power.