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.
The new majority opinion transformed Citizens United into a vehicle for rewriting decades of constitutional law in a case where the lawyer had not even raised those issues.
As ThinkProgress previously explained, Kennedy is widely viewed as a moderate conservative, but this perception is inaccurate. Although Kennedy does sometimes deviate from conservative orthodoxy on social or on criminal justice issues, he is a hard line conservative on economic justice. Kennedy is a zealous supporter of forced arbitration, a practice that allows corporations to force their workers and consumers into a privatized arbitration system that overwhelmingly favors corporate parties. He cast the key vote against Lilly Ledbetter and against equal pay for many women in the workplace. He cast the key fifth vote empowering corporations to immunize themselves from consumer class actions. And, of course, he also voted to install install George W. Bush as president.