But notice what that second rationale does. If the argument is just federalism, the court is saying: Each state decides — and we, the court, are out of here. But if the argument is equal protection, one question is left hanging. Why should equal protection apply only in states that recognize gay marriage? Why doesn’t it apply equally — indeed, even perhaps more forcefully — to gays who want to marry in states that refuse to marry them?

If discriminating (regarding federal benefits) between a gay couple and a straight couple is prohibited in New York where gay marriage is legal, by what logic is discrimination permitted in Texas, where a gay couple is prevented from marrying in the first place?

Which is exactly where the majority’s second rationale leads — nationalizing gay marriage, the way Roe nationalized abortion. This is certainly why David Boies, the lead attorney in the companion Proposition 8 case, was so jubilant when he came out onto the courthouse steps after the ruling. He understood immediately that once the court finds it unconstitutional to discriminate between gay and straight couples, nationalizing gay marriage is just one step away.