George Mason law professor David Bernstein wonders if Roberts bailed from the dissenting opinion at the last moment:
Scalia’s dissent, at least on first quick perusal, reads like it was originally written as a majority opinion (in particular, he consistently refers to Justice Ginsburg’s opinion as “The Dissent”). Back in May, there were rumors floating around relevant legal circles that a key vote was taking place, and that Roberts was feeling tremendous pressure from unidentified circles to vote to uphold the mandate. Did Roberts originally vote to invalidate the mandate on commerce clause grounds, and to invalidate the Medicaid expansion, and then decide later to accept the tax argument and essentially rewrite the Medicaid expansion (which, as I noted, citing Jonathan Cohn, was the sleeper issue in this case) to preserve it? If so, was he responding to the heat from President Obama and others, preemptively threatening to delegitimize the Court if it invalidated the ACA? The dissent, along with the surprising way that Roberts chose to uphold both the mandate and the Medicaid expansion, will inevitably feed the rumor mill.