The joint dissent issued by Justices Scalia, Kennedy, Thomas, and Alito certainly reads as though it were written to be the majority opinion. Among other things, the joint dissent’s discussion of the taxing power doesn’t respond to the Chief Justice’s opinion (indeed, I think it never even cites it). Rather, it addresses only the government’s argument. By contrast, the Chief’s opinion repeatedly takes issue with the joint dissent. This strongly suggests to me that the joint dissent was written first, as the proposed majority opinion, but failed to garner the fifth vote from the Chief.
The fact that the joint dissent (see slip op. at 13-16) repeatedly refers to Justice Ginsburg’s views on the Commerce Clause issue as the “dissent” reinforces my impression—all the more so as the dissenters don’t undertake to point out that their views combined with the Chief Justice’s establish a majority on the Commerce Clause point.
Addendum: One serious problem with the above theory is that it’s difficult to reconcile with the fact that the Chief would have assigned the majority opinion in the first place. An alternative theory is that the joint dissenters wrote their opinion as they did, after the Chief circulated his draft, in order to signal their deep dissatisfaction with his draft. I now lean towards this alternative theory.
2nd Addendum: Then there’s a compelling third theory, which is really only an elaboration of the first in a way that solves the apparent problem with it.
In any event, enough of what-might-have-been. The imperative now needs to be to defeat Obamacare politically this November.