Mr. Verrilli was trying to make the point that a decision not to buy broccoli doesn’t increase the price others must pay for broccoli in the same way that a decision to forgo health insurance increases the premiums others must pay for health insurance. But it seems to me that a succinct answer to Justice Scalia’s question is that the commerce clause would not limit Congress’s ability to regulate broccoli — if members of the House and Senate were crazy enough to pass legislation requiring all of us to eat green vegetables and if that were deemed a rational way to regulate commerce. The same could be said of health clubs.

A lengthy Wall Street Journal editorial last week argued that “the reality is that every decision not to buy some good or service has some effect on the interstate market for that good or service.” That may well be true, and Mr. Verrilli should have admitted it rather than getting entangled in unconvincing semantics.

That doesn’t mean we would all be required to eat broccoli. Congress has the constitutional power to pass many bills that would strike most people as idiotic, but as a popularly elected assembly, it doesn’t. The Supreme Court itself has said: “The principal and basic limit on the federal commerce power is that inherent in all Congressional action — the built-in restraints that our system provides through state participation in federal governmental action. The political process ensures that laws that unduly burden the states will not be promulgated.” And absurd bills like a broccoli mandate are likely to fail other constitutional tests.