Earlier today I mentioned this interesting post by Randy Barnett at The Volokh Conspiracy concerning the Justice Department's litigation strategy to defend the the ACA's individual insurance mandate as a valid exercise of Congress's power to tax under the General Welfare Clause. Jack Balkin has responded with this thoughtful post at Balkinization -- which not only discusses the merits of Barnett's claims, but also what they say about the nature of American Constitutional Development (that is, the process by which the meaning of our Constitution changes over time). Both posts deserve a close read.
It should be noted that this is (at least) round three for Professors Barnett and Balkin on the subject of the ACA. They squared off here in the New York Times's Room for Debate blog, and they have co-authored opposing amicus briefs in Virginia v. Sebelius.