Predicting a Supreme Court decision is almost as risky as the predicting the identity of a lottery winner. There were only a few people who thought that Chief Justice John Roberts would vote to affirm the constitutionality of the Affordable Care Act. I was not one of them, but I had a lot of company.
Keep in mind that the Court is considering two cases on gay marriage. Each case has distinct constitutional issues. The main argument against Proposition 8, which bans gay marriage in California, revolves around the 14th Amendment. The plaintiff in that case argues that the equal protection clause forbids discrimination and that Prop 8 discriminates against same-sex couples.
The constitutional argument in the other case, U.S. v Windsor, is that Congress didn't have the constitutional power to enact the Defense of Marriage Act. DOMA states that the federal government only legally recognizes traditional marriage. But Article 1, Section 8 of the Constitution, which lists Congress' powers, doesn't give Congress the authority to regulate marriages.
Assuming that the four liberal justices rule that Prop 8 and DOMA are unconstitutional and the four conservative justices vote that the laws are acceptable, the deciding vote would be Justice Anthony Kennedy. In the oral argument in the Prop 8 case Tuesday, Justice Kennedy seemed sympathetic to the pro-gay rights argument. Also, Justice Kennedy came down on the pro-gay rights side in the last major case on this issue to come before the Court, Lawrence v. Texas.
In the oral arguments in the Prop 8 case, the justices appeared unsure of themselves. However, many of the justices were openly hostile to DOMA during the arguments on that case.
People in power love to get things done by not doing anything. The Court could also get rid of this hot potato by ruling on technical grounds that the supporters of Prop 8 and DOMA don't have the legal standing to be a party in the suits. In the Prop 8 case, the original defendant was the state of California. The state dropped out of the case after a lower court ruling against Prop 8, and there is a question on whether the supporters of Prop 8 have the right to bring the case to court without the blessing of the state. In the DOMA case, the Obama administration is arguing against DOMA, not for it. In that case, supporters of the law may not have the legal standing either.
Gay rights activists hope the Court openly nullifies Prop 8 and DOMA on constitutional grounds. But if the court rules that defendants in both cases don't have legal standing to defend the laws, supporters of gay marriage would benefit. In the Prop 8 case, the ruling of the 9th U.S Circuit Court of Appeals would stand, which nullified the California law. If the Court refuses to decide the DOMA case, the anti gay marriage federal law would stand, but the Obama administration would not enforce it. The justices may reason that if the parties of record don't want to defend the laws, there's no legal dispute and no case.
One thing is guaranteed: The court probably will not issue a ruling on the cases until June. So we'll have plenty of time to opine.