As he and his law clerks worked on the tax issue, the Chief Justice discovered that the opinion “wouldn’t write.” He couldn’t come up with an account of the tax power — persuasive to him — that would invalidate the ACA. Perhaps his difficulty in getting an opinion that “would write” was influenced by institutional concerns about the long-term standing of the Court, or somewhat different institutional concerns about his ability to pursue a conservative legal agenda on matters more important to him over the long run. And, though less plausibly, perhaps these institutional concerns came to have more salience as liberals mounted their post-argument challenges to an anticipated decision invalidating the ACA. But, I would guess, those things operated — if they did, and I’m skeptical — well below the surface. Mostly, the Chief Justice found that the opinion wouldn’t write.

On this view, the Chief Justice didn’t “switch” his vote, because he hadn’t been firmly committed to the view that the ACA couldn’t be defended under the tax power. Once he indicated his view on the tax issue, the rest of the opinions fell into place. The four now-dissenters assembled their separate contributions into their joint dissent and tacked on some discussion of the Chief Justice’s new position.