As co-blogger Will Baude points out, today the US Court of Appeals for the Tenth Circuit became the first federal appellate court to strike down a state law banning same-sex marriage since the Supreme Court’s landmark decision in United States v. Windsor last year. The opinion is available here. Ruthann Robson of the Constitutional Law Prof blog has a helpful summary.

There have been numerous federal trial court decisions striking down state laws restricting marriage to opposite-sex couples over the last few months. But this decision is significant because it is the first such ruling by an appellate court. It is also notable because there is a lengthy and detailed dissent by Judge Paul Kelly, who has now become the first judge since Windsor to conclude that a state law banning same-sex marriage does not violate the Constitution. Kelly’s opinion suggests that there is not a clear consensus in the federal judiciary about either the implications of Windsor or the same-sex marriage issue more generally.

As Robson points out, the Tenth Circuit majority ruled that the challenged Utah law is unconstitutional because it restricts the “fundamental” right to marriage under the Fourteenth Amendment, which subject it to tight “strict scrutiny.” Such laws must be narrowly tailored to the advancement of a “compelling state interest.” The court assumed that three of the interests asserted by Utah – (1) “fostering a child-centric marriage culture that encourages parents to subordinate their own interests to the needs of their children”; (2) “children being raised by their biological mothers and fathers—or at least by a married mother and father—in a stable home”; and (3) “ensuring adequate reproduction” are indeed compelling. But it also ruled that the law was not narrowly tailored to their advancement.

For reasons I explained in this post, I am skeptical about the validity of the argument embraced by the Tenth Circuit majority. But I do believe they reached the right result, because laws restricting marriage to opposite-sex couples are an example of unconstitutional sex discrimination. This reasoning was endorsed by the district court opinion affirmed by the Tenth Circuit (though it also endorsed other constitutional arguments against laws restricting marriage to opposite-sex couples).

Be that as it may, today’s decision is an important victory for advocates of same-sex marriage. But Judge Kelly’s dissent suggests that the legal battle over the issue is far from over. The question is likely to return to the Supreme Court, quite possibly sooner than many of us at first anticipated.

UPDATE: Josh Blackman has interesting posts on various aspects of the ruling here, here, and here. But I don’t agree with his claim that the decision suggests that “tiers of scrutiny are largely irrelevant.” Much of the majority’s reasoning turns on the claim that, because marriage is a fundamental right, the Utah law is subject to very stringent “strict” scrutiny that is difficult to pass. Judge Kelly, in dissent, reaches a different conclusion because he believes that only minimal “rational basis” scrutiny applies. Tiers of scrutiny still often determine the burden of proof the government must meet to justify its law. And, as is often the case in litigation, the burden of proof determines the outcome.

UPDATE #2: It is not entirely clear whether the majority concluded that the three state interests mentioned actually are compelling, or merely assumed that they are for the sake of argument. The wording of the opinion uses the phrase “we will assume,” which strongly suggests the latter (though “assume” can sometimes indicate an assumption made because it is considered likely to b e true). To be on the safe side, I have changed the phrasing in the post to “assumed,” since the majority at the very least did that much.