Legal scholars and political activists have debated the constitutionality of the recent health care legislation for more than a year now. This debate received widespread media attention when the Affordable Care Act passed Congress last March and again when a Virginia district judge declared portions of the act unconstitutional last month. For all the words spilled on this subject, however, no one has made the most essential point: Both sides are right.

No, I do not mean that the Affordable Care Act is both constitutional and unconstitutional. But the principal contentions of both sides — the contentions that both camps assume lead inexorably to their own preferred conclusions — are equally true. Opponents of the act are correct that, if Congress can force individuals to purchase health insurance, it can, for all practical purposes, do anything. For courts to uphold the act would thus cast aside a cherished principle of American constitutional law — that the national government is one of limited powers, with everything else left to the states.