So we may ask: is there a constitutional limiting principle that would allow Massachusetts to impose that mandate but prevent it from requiring its residents to join health clubs or buy broccoli? There are of course constitutional limits to any power of government. Neither the indirect mandate of taxation nor any more direct mandate may be discriminatory or irrational, neither may deny due process, and each must serve some proper purpose of government. But are there any special limiting principles that would prohibit a state requiring broccoli purchase in a rational and fair way?

No. We are protected from silly state mandates not because the Constitution rules them out but because politics does. No state legislature would dare to make broccoli purchase compulsory unless, for some hard-to-imagine reason, this was plainly the only way to avert some economic catastrophe. The role of democratic politics in protecting citizens against legislative corruption or stupidity does not depend on whether the legislature wants to require or forbid economic activity, however. Voters would be no less outraged by a state legislature’s decision to ban automobiles altogether than by its decision to make them buy electric cars.

If we do not need a limiting constitutional principle to stop a state from outrageous economic legislation, we do not need any such principle to stop the national Congress, within its proper sphere, either. The Court can allow Congress, as it allows Massachusetts, to mandate health insurance without finding a constitutional barrier to a national compulsory broccoli purchase. Politics supplies the appropriate check in both cases. So we must turn to the genuinely important question, the second question I distinguished. What is Congress’s proper sphere of control in health care matters?