If you would read a detailed discussion of who decided what when concerning the Supreme Court's health care law decision, Jan Crawford's article for CBS News is your choice. As Jan Crawford Greenberg she did SCOTUS analysis for the PBS News Hour for 9 years, and she is the real deal.
It turns out Chief Justice Roberts did change his mind. He was initially against it, and later changed his mind and decided to support it. You are unlikely to read a better discussion of his actions, unless at some point he decides to write them up himself. Hat tip to The Weekly Standard for the link.
