Chief Justice John Roberts argued, in NFIB v. Sebelius, that the Affordable Care Act exceeded Congress’s commerce power. The individual mandate to purchase insurance was not authorized by the Necessary and Proper Clause, he reasoned, because it involved a “great substantive and independent power.” He did not explain how one could tell what constituted such a power. This limitation was worked out in more detail by amici, and Roberts may have been gesturing toward their argument. This essay will look to the antecedents of Roberts’s argument to try to make better sense of what he said. This strategy will fail. There is no way to make this argument look good. It is a placeholder for a raw intuition that the law’s trivial burden on individuals was intolerable, an outrageous invasion of liberty, even when the alternative was a regime in which millions were needlessly denied decent medical care.