Unlike growing wheat or marijuana, the decision not to buy medical insurance does not produce anything, let alone a commodity traded between states. Maybe so, say ObamaCare’s defenders, but that decision has an impact on the demand for insurance and on the health care market (one-sixth of the economy!), which the federal government is trying to control in the same way that it tries to control the marijuana trade (with similar prospects of success).

This sort of reasoning leaves nothing beyond the reach of Congress, since anything you do (or don’t do) can be said to affect interstate commerce. In its 1995 decision overturning a federal ban on possessing guns near schools, the Supreme Court cautioned against the temptation “to pile inference upon inference in a manner that would bid fair to convert congressional authority under the Commerce Clause to a general police power of the sort retained by the States.” That kind of analysis, the Court warned, threatens to “obliterate the distinction between what is national and what is local.”

In a recent Heritage Foundation paper, Georgetown University law professor Randy Barnett and two co-authors note that the decision upholding wheat quotas does not mean “Congress can require every American to buy boxes of Shredded Wheat cereal on the grounds that, by not buying wheat cereal, non-consumers were adversely affecting the regulated wheat market.” Likewise, federal regulation of carmakers does not mean “Congress could constitutionally require every American to buy a new Chevy Impala every year.”