The dissatisfaction of conservatives grew as they studied the decision and found clues that the chief justice might initially have been in the majority to strike down the law, only to switch sides. A report from CBS News on Sunday that he had changed his mind added to the anger.

In his opinion, Chief Justice Roberts said the health care law’s requirement that most Americans obtain insurance or pay a penalty could be justified as a tax, and the court’s four liberal members — Justices Ruth Bader Ginsburg, Stephen G. Breyer, Sonia Sotomayor and Elena Kagan — joined that part of the ruling. But the chief justice also said that the requirement could not be justified under Congress’s power to regulate interstate commerce, in agreement with the other three conservatives — Justices Antonin Scalia, Clarence Thomas and Samuel A. Alito Jr. — and the court’s usual swing member, Justice Anthony M. Kennedy.

It was the dissenting opinion of those four justices that attracted the most attention, as it was studded with hints that they had once been on the winning side across the board. The dissenters did not, for instance, formally join any part of Chief Justice Roberts’s opinion, though they agreed with him on several points. The usual practice would have been to note that the dissenters concurred in part in the court’s judgment. Nor did they meaningfully engage with the chief justice’s opinion where the two sides disagreed, which could be a sign of hurry or frustration.

The joint dissent also referred to the opinion of Justice Ginsburg, which concurred in part and dissented in part from the chief justice’s opinion, simply as her dissent, suggesting that it was once only that. Justice Ginsburg’s opinion was quite acid in its discussion of the commerce clause ruling, a tone that seemed at odds with the liberal side’s overall victory.

But there is also evidence pointing the other way. The argument that carried the day — that the individual mandate could be considered a tax — was one the chief justice pursued at the arguments in March.

It is not particularly unusual for justices to change their minds while writing and exchanging drafts. Laurence H. Tribe of Harvard Law School said that “the more it happens, the more it gives you confidence that there was a serious exchange of ideas.”