In researching the Supreme Court amicus brief I wrote with Richard Epstein and Cato’s Ilya Shapiro on severability, I reviewed virtually every major Supreme Court severability decision back to Marbury v. Madison (1803). Looking back on those decisions, I am certain that striking down the individual mandate in Obamacare would have presented the Court with the most complex and difficult severability analysis in its history. Indeed the case seems almost tailor-made to test the limits of the Court’s severability doctrine to the breaking point. This is because (as we argued in our brief) the individual mandate is so interwoven with the other key provisions of the law (Titles I and II) that they could not have functioned as intended without the mandate. The 11th Circuit Court of Appeals decision to strike the mandate and leave the rest of the law in place was clearly incorrect. So the only good option to striking down the whole law was to strike down the core provisions and leave a shell of ancillary provisions in place. But Justice Antonin Scalia made it very clear during oral argument he would not support that outcome…

Roberts may have concluded that there was no prospect of five votes for a defensible outcome on the issue of severability, and switched sides in order to avoid reaching the issue at all. This is all pure speculation, of course, but it’s at least as plausible as all the other speculation you’ve heard in the last week about why Roberts voted the way he did.