During last month’s Supreme Court oral argument over the fate of the Defense of Marriage Act, Justice Anthony Kennedy suggested his willingness to vote against the law on federalism grounds, thereby providing a likely fifth vote against DOMA and a major win for the gay rights movement.

So why is liberal legal columnist Linda Greenhouse of The New York Times so disappointed? Because, she writes, “what reverberated from the bench was the discordant music of federalism – the federalism that almost sank the Affordable Care Act.” Here’s Greenhouse writing in a recent column:

Ever since last week’s frustrating Supreme Court argument in the Defense of Marriage Act case, I’ve been wondering whether the attack on DOMA will turn out to be a constitutional Trojan horse. It may bring victory: the demise of a spiteful federal statute, enacted by an opportunistic Congress and signed into law 17 years ago by a cowardly Bill Clinton. But at what price?...

[S]triking down DOMA on federalism grounds is a truly bad idea, and the campaign for marriage equality would be worse off for it. To explain the argument is to reveal its dangers. A ruling that left the states to their own devices when it comes to marriage would take the equal protection guarantee out of the picture.

I’m not sure Greenhouse entirely understands how federalism works in this case. The federalist argument against DOMA is that Congress lacks any enumerated power under the Constitution to enact this particular piece of legislation. If the Supreme Court agrees with that argument, then the overreaching federal law must fall. That’s it. End of story.

Whether or not the states should be left “to their own devices” on gay marriage is a totally separate issue hinging on a totally separate constitutional question: Does the Equal Protection Clause of the 14th Amendment prevent the states from banning gay marriage? If the answer to that question is yes, then the federal courts have an obligation to strike down those bans.

Put simply, a federalist ruling against DOMA says nothing about the constitutionality of state laws precisely because DOMA is not a state law, it’s a federal one. It’s not that complicated.