Yesterday, the United States Supreme Court granted review in two cases that have the potential to determine the constitutional status of the right to gay marriage -- Hollingsworth vs. Perry (Proposition 8) and United States vs. Windsor (Section 3 of the Defense of Marriage Act). However, in its order granting review in these two cases (along with some other unrelated cases), the United States Supreme Court added its own questions to these cases.
By way of background, under Supreme Court rules, when a party asks for review of a case, they are required to list the question or questions which they think the case raises that need an answer from the Supreme Court. Advocates try to frame these questions in a way that make them seem important and worthy of the Supreme Court's time. When the other side files its response, it is not unusual for the other side to try to reframe the "questions presented" by the case to make the issues seem less interesting and to add other questions that need to be reached in order to reach the mertis of the question suggested by the other side. When the Supreme Court opts to review the case (it takes four Justices voting to take the case), it can agree to hear all of the questions presented by the party seeking review or just some of the questions. It can also agree to add some of the questions from the response or add questions of its own.
In United Staes v. Windsor, the question presented in the petition from the Solicitor General was "[w]hether Section 3 of DOMA violates the Fifth Amendments guarantee of equal protection of the laws as applied to persons of the same sex who are legally married under the laws of their states." In Hollingsworth vs. Perry, the question presented in the petition from the sponsors of Proposition 8 was "[w]hether the Equal Protection Clause of Fourteenth Amendment prohibits the State of California from defining marriage as the union of a man and a woman."
In both cases, however, the Supreme Court opted to add an additional question or questions. For Windsor, one of the questions is an improtant but technical question about the posture of the parties (and when the Supreme Court will hear a case on the merits). While the other question in Windsor and the additional question in Perry is also a procedural question, it is actually a rather big constitutional issue for the judicial branch.
One of the basic rules of the American judicial system is that courts only hear cases in which a party has a real substantial issue -- frequently referred to as standing. Just because I might personally think that a recent ordinance passed by my city council is the worst ordinance in history, unless that ordinance actually violates my rights or otherwise harms me, I can't challenge the validity of that law in court. Likewise, unless that law provides me a personal substantial benefit giving me a different interest in upholding the law than the government or the rest of the public, I don't have the right to intervene in a court case challenging that law even if I like the law and think the government isn't doing its job in defending the law.
These two cases involve the unique circumstance in which the executive branch officials charged with the official duty of defending the government (and the validity of federal (in Windsor) and California (in Perry) laws have decided that the law is indefensible. in Windsor, the "Bipartisan Legal Advisory Group" of the House of Representatives intervened to defend the law in the lower courts. The Supreme Court now asks whether that group has standing to defend the law. In Perry, the persons who originally circulated the petition to put Proposition 8 on the ballot (the official sponsors) intervened to defend the law in the lower courts. The Supreme Court now asks whether these individuals have standing to defend the law.
The bottom line issue presented by both of these questions is whether the legislative branch/power can step into defend a law when the executive branch/power refuses to defend/adequately defend a statute. Given that this Supreme Court has been somewhat ruthless in narrowing who has "standing" to pursue a case, this clash between the branches could very easily become the central issue in the two cases with a majority of the Supreme Court deciding that they should not reach the merits of either case (leaving the constitutionality of bans on gay marriage for another day when the trend in public opinion might be clearer), and should instead use these cases to substantially restrict the circumstance in which the legislature (or legislators) can participate in a case in an effort to override an executive branch decision.