Jeffrey Toobin in the New Yorker explains how John Roberts orchestrated the Citizens United decision:
A private drama followed which in some ways defined the new Chief Justice to his colleagues. Roberts assigned the Citizens United opinion to himself. Even though the oral argument had been dramatic, Olson had presented the case to the Court in a narrow way. According to the briefs in the case—and Olson’s argument—the main issue was whether the McCain-Feingold law applied to a documentary, presented on video on demand, by a nonprofit corporation. The liberals lost that argument: the vote at the conference was that the law did not apply to Citizens United, which was free to advertise and run its documentary as it saw fit. The liberals expected that Roberts’s opinion would say this much and no more.
At first, Roberts did write an opinion roughly along those lines, and Kennedy wrote a concurrence which said the Court should have gone much further. Kennedy’s opinion said the Court should declare McCain-Feingold’s restrictions unconstitutional, overturn an earlier Supreme Court decision from 1990, and gut long-standing prohibitions on corporate giving. But after the Roberts and Kennedy drafts circulated, the conservative Justices began rallying to Kennedy’s more expansive resolution of the case. In light of this, Roberts withdrew his own opinion and let Kennedy write for the majority. Kennedy then turned his concurrence into an opinion for the Court.
As the senior Justice in the minority, John Paul Stevens assigned the main dissent to Souter, who was working on the opinion when he announced his departure, on April 30th. Souter wrote a dissent that aired some of the Court’s dirty laundry. By definition, dissents challenge the legal conclusions of the majority, but Souter accused the Chief Justice of violating the Court’s own procedures to engineer the result he wanted.
Roberts didn’t mind spirited disagreement on the merits of any case, but Souter’s attack—an extraordinary, bridge-burning farewell to the Court—could damage the Court’s credibility. So the Chief came up with a strategically ingenious maneuver. He would agree to withdraw Kennedy’s draft majority opinion and put Citizens United down for reargument, in the fall. For the second argument, the Court would write new Questions Presented, which frame a case before argument, and there would be no doubt about the stakes of the case. The proposal put the liberals in a box. They could no longer complain about being sandbagged, because the new Questions Presented would be unmistakably clear. But, as Roberts knew, the conservatives would go into the second argument already having five votes for the result they wanted. With no other choice (and no real hope of ever winning the case), the liberals agreed to the reargument.