The justices who were skeptical of the individual mandate kept asking the administration to supply a “limiting principle”: If the mandate was permissible, what wouldn’t be? But the proponents of the mandate’s constitutionality make the flip-side argument: If the justices can strike down the mandate, what’s the limiting principle on them? Are the justices to strike down all of post–New Deal government? Even conservatives and libertarians who might be thrilled at the idea of their doing just that may think that the mandate goes beyond anything we have seen before, and therefore suspect that some constitutional principle makes it particularly troublesome.
In this NRO article, I borrow heavily from Michael Greve in outlining what a two-sided limiting principle — one that justifies holding the mandate unconstitutional without authorizing wide-ranging judicial discretion — might look like. The short version: The mandate can’t be “proper” under the necessary-and-proper clause because it violates an anti-commandeering principle that is part of the constitutional structure.