Slightly over eight months ago, the United States Supreme Court issued one opinion (in Windsor v. United States) striking down Section 3 of the Defense of Marriage Act and another opinion (in Perry v. Hollingsworth) declining to consider whether there was a constitutional right to same-sex marriage. The net result of these two opinions was to invalidate Section 3 of DOMA (banning federal recognition of same-sex marriages) but to leave intact Section 2 of DOMA (allowing states to refuse to recognize same-sex marriages performed in other states) and state law bans on in-state same-sex marriages (except for California's ban). The reasoning in Windsor, however, inspired a new wave of challenges in state and federal courts to Section 2 of DOMA and to state bans on in-state marriages.
Since then, particular in the last three months, federal district courts have started to issue rulings on these cases. As of this point, federal courts in Kentucky, Oklahoma, Utah, Texas, and Virginia have struck down state law bans on same-sex marriages and a federal court in Ohio has struck down Section 2 of DOMA, finding that Ohio had to recognize marriages performed in other states. Furthermore, the state attorney generals in Nevada, Oregon, and Virginia have concluded that there is no valid legal basis to defend their state laws banning same-sex marriage.
Going forward, all of these decisions are currently being challenged on appeal. The first round of arguments will be the Tenth Circuit (which includes both Oklahoma and Utah) in April. Given normal court practices, the earliest likely date for an opinion from the Tenth Circuit would be August or September. The losing party would then have the option of asking for rehearing or simply proceeding to ask for the Supreme Court to review the case. My hunch is that, if the losing party in any of the Circuit Courts asks for rehearing by the entire court, there is a decent chance that they will get it, considering the significance of this issue. (In the Court of Appeals, cases are normally heard by a three-judge panel. While parties can request that the entire court -- or for the Ninth Circuit, a panel of about half the court -- rehear the case after the initial opinion, the full court denies that request almost all of the time. Given this practice, it is probably more likely that a request for rehearing would be declined, but the significance of these issues is likely to cause the judges to give the request closer consideration than in most cases.)
The key date for all of the pending appeals is probably around September 1 for the mandate from the Court of Appeals. The losing party on appeal has ninety days after the issuance of the mandate (normally issued within days of the denial of rehearing or the expiration of time to request rehearing) to file with the Supreme Court. The winning party has thirty days to file a response to the any petition filed with the United States Supreme Court. However, both parties can request extensions. Once a case is filed in the Supreme Court, the key day is in early January. If the response is filed by early January, the case can still be considered at a January conference and argued on the April argument calendar. If a case goes to the first February conference, the case will probably be bumped to the a fall argument calendar.
Given how tight the schedule is, I think it is unlikely that the Supreme Court will consider any cases on the merits of same-sex marriage until the fall of October 2015, potentially putting any decision on this issue into the Spring of 2016. What the Supreme Court does when these cases reach them will depend in large part on what happens in the various Courts of Appeal. If all of the Circuit Courts take an expansive reading of Windsor (as the District Courts have so far), there is a good possibility that the Supreme Court will decline to take a case on the state law bans, and instead take a case like the Ohio case challenging Section 2 of DOMA. Such an approach would satisfy those on the Supreme Court who want to proceed cautiously on this issue until such time as a decision authorizing same-sex marriage is almost an afterthought (i.e. when almost every state is already allowing same sex marriage). If a split develops in the Circuit Courts, however, the Supreme Court would be likely to take a case on the ultimate issue of whether there is a constitutional right to same sex marriage sooner.
The steady march of rulings by federal courts striking down state law bans has, to some extent, started to produce a reaction in "red" states with legislatures considering (but so far not enacting) religious conscious laws designed to allow folks to opt out of providing wedding-related services to those same-sex couples planning a wedding. To date, these laws have been extremely broadly written (allowing discrimination against homosexuals generally) which has led to their failure. I would expect to see a second version of these laws coming forward soon that will be more narrowly tailored to limit them to certain types of services.