In Iowa, as in California but not Massachusetts, Supreme Court justices face retention elections periodically - every 8 years in Iowa, every 12 years in California. This means that a justice who supported Varnum v. Brien, the same-sex marriage decision, is taking some actual risk that there will be an organized campaign to boot him or her. Per Nate Silver at FiveThirtyEight, support for same-sex marriage is increasing about 2 points a year. Nate's model claims that Iowans will vote for same-sex marriage in 2013. (Electoral outcomes would presumably be more positive for "a justice who supports same-sex marriage among other qualities" than "same-sex marriage," but if you know something about public opinion that contradicts this, you should feel free to jump in.) You might thus predict that the further away a justice's retention election, the easier it would be for that justice to support Varnum v. Brien. In fact, of the seven justices who unanimously voted for the decision, three have retention elections in 2010, including one who was only appointed in 2008. That suggests they were willing to risk their own positions on the court for same-sex marriage, which I just find very endearing. And brave.