As you've heard by now, the Supreme Court today declined to hear a set of five cases involving state bans on same-sex marriage, from Virginia, Utah, Oklahoma, Indiana, and Wisconsin. In all these cases, the appeals court had overturned the state's ban, and now same-sex marriages are legal not only in those states, but also soon in the six other states covered by the 4th, 7th, and 10th Circuits (Wyoming, Colorado, Kansas, West Virginia, North Carolina, and South Carolina).
Like many other people, I've already written today that the legal argument over marriage equality is now all but over. The way it presumably will play out from this point forward is that one of the more conservative circuit courts will issue a ruling upholding a state ban on same-sex marriage, and the Supreme Court, presented with this conflict between circuits, will take the case to settle it. And in the wake of today's ruling, it's hard to see how they (and by "they" I mean Anthony Kennedy) would rule that state bans are in fact constitutional, when they just effectively overturned bans in 11 states. (If you're looking for a primer on what happened today, this one from Vox is good.)
But there is one scenario by which what today seems like an inevitable forward movement for marriage equality could be undone, and it may be the only hope conservatives have left. It involves a Republican winning the White House in 2016 and a liberal justice retiring, to be replaced by a conservative.
This isn't some remote possibility. We have no idea what the election of 2016 will be like, and while as a liberal you probably think that the current crop of Republican contenders are a bunch of bozos, people thought that about any number of people who ended up winning the White House (see Bush, George W.). As of now, Ruth Bader Ginsburg is 81, Stephen Breyer is 76, Sonia Sotomayor is 60, and Elena Kagan is 54. Any one of them could retire for any number of reasons. And once President Rand Paul appoints Ted Cruz to take that retiree's place, things look very different.
Of course, it's possible that, now with 30 states plus D.C. having marriage equality, and who knows how many gay couples even in some very conservative places like Utah and South Carolina getting married, even a future conservative majority on the Court might decline to turn back the clock. It's also possible that a Democrat will win in 2016, or that there will be no retirements from the liberals until the next Democratic presidency. I also think that within a few years, even Republican-appointed justices are going to have to pledge to uphold marriage equality—though they may move through a phase of strategic obfuscation as they have on abortion. But even though today's rulings are an incredibly big deal and progress toward marriage equality in every state may be inexorable, there's at least one more hurdle that needs to be overcome.