The Supreme Court didn't make gay marriage legal in all 50 states on Tuesday, but Justice Anthony Kennedy's opinion in United States v. Windsor gave us a clear sign of how it will happen. Shannon Minter, legal director of the National Center for Lesbian Rights, tells The Atlantic Wire, "While today's ruling applied only to DOMA, most of the reasoning and analysis would apply equally to state marriage bans, and it is likely we will see more challenges to those state bans in the coming years and that the Supreme Court will be asked to rule on the constitutionality of all state marriage bans in the not too distant future." Kennedy said the Defense of Marriage Act, which defines marriage as between a man and a woman, not only violated federal deference to states' tradition of defining marriage, it also was passed to express disapproval of gay people. In his angry dissentJustice Antonin Scalia warned that if it's not OK for the federal government to do treat gay people like that, the court will eventually find it's not OK for the states to do that, either. Gay marriage supporters hope Scalia's right. As Minter said, "The writing is on the wall!"

"It's a very big day obviously," Loyola University law professor Douglas NeJaime said. "It's two big steps forward for the same-sex marriage cause. But the interesting question is what happens down the road, because the constitutionality of state bans has not been resolved." Kennedy's opinion had a "really important marriage on the dignity and equality of same-sex couples." Hours after the decision, the ACLU, which brought the Windsor case to the Supreme Court, announced a $10 million campaign to do exactly what Scalia feared. "The next step is the battle to overturn 30 state DOMAs, state by state," the ACLU's Anthony D. Romero told The New York Times' John Schwartz. "Justice Scalia is finally right — on this one." The ACLU is hiring Steve Schmidt, who was John McCain's 2008 presidential campaign manager, to run the effort.

DOMA is unusual, Kennedy said, because usually the federal government accepts state definitions of marriage. Instead, it takes away those benefits. "This is strong evidence of a law having the purpose  and effect of disapproval of a class recognized and protected by state law." Scalia scoffed that the court was "leaving the second, state-law shoe to be dropped later, maybe next Term." NeJaime says next term might be a little too soon, but there are a few cases that present the question of whether state constitutional bans are constitutional. Sevcik v. Sandoval challenges Nevada's gay marriage ban, and Jackson v. Abercrombie challenges Hawaii's. The Ninth Circuit Court of Appeals put these cases on hold until the Supreme Court decided on DOMA and Prop 8.

There are parts of Kennedy's opinion that state-level opponents of gay marriage can look to. At SCOTUSblog, Tejinder Singh explains that while Section 3 of DOMA — the marriage is only for boy + girl part — was struck down, Windsor didn't address Section 2 of DOMA, which says other states do not have to recognize a gay marriage granted in another state. If or when a Section 2 case comes, Singh says, "both sides could find support in today's opinion. Challengers to Section 2 would argue that it is rooted in the same 'bare animus' that the Court held characterizes Section 3. Defenders of Section 2 would argue that Section 2 is really about the states' rights to define marriage, which today's opinion supports."

As The Atlantic Wire explained after the cases' oral arguments in March, the Supreme Court's decision is going to create a lot of immediate problems. Gay couples legally married in New York will now get all their federal benefits there. But what if they move to Mississippi? The National Center for Lesbian Rights's Minter explained that some states recognize common law marriages while others don't, and the federal government only recognizes them when the state does. But NeJaime said it could be more complicated. New York doesn't have common law marriages, but if a common law married couple from South Carolina moves to New York, New York will recognize their marriage. That's because New York doesn't think it has a strong public policy interest in not recognizing common law marriages. But that's clearly not the case for gay marriage in states like Mississippi. It's possible a married gay couple in New York will move to Mississippi and lose recognition of their marriage.