The question presented in United States v. Windsor is whether Section 3 of the Defense of Marriage Act (DOMA) violates the Fifth Amendment’s guarantee of equal protection. Why, then, are some of us talking about federalism? It’s a fair question.
In an equal protection case, courts are called upon to weigh the weight of the government’s asserted interest and evaluate whether the allegedly discriminatory policy is sufficiently related to that interest. So, for instance, under the rational basis test, a court considers whether the challenged policy is rationally related to a legitimate government interest; under intermediate scrutiny a court considers whether the challenged policy is substantially related to an important government interest; and so on. Under each test, courts must consider the nature and weight of the asserted governmental interest — and not just any interest will do. Animus or the naked desire to harm or oppress another group won’t do, nor will any other interest that is not properly pursued by the government — and that is where federalism comes in.
Because the federal government is a government of limited and enumerated powers, the range of interests it may assert in defense to an equal protection challenge is necessarily limited. It cannot assert just any governmental interest to sustain a policy, such as Section 3 of DOMA, because not all governmental interests are federal interests. Whether or not one believes the range of federal interests is limited to the objects of enumeration in the Constitution, there should be no doubt that the federal government, lacking a plenary police power, does not have recourse to the same range of potential interests as do state governments. And those interests that remain may only justify so much. Efficient administration of a federal program may suffice (at least under rational basis), but it’s hard to argue that Section 3 of DOMA is about the efficient administration of anything, particularly since in some applications it will actually make program administration more difficult and it costs the federal treasury millions. (See, e.g., here.)
Incorporating federalism concerns into Equal Protection analysis means that there are certain policy choices states may make, but that the federal government many not. As a consequence, the Supreme Court could well conclude that California’s Proposition 8 survives Equal Protection challenge, but Section 3 of DOMA does not. Should the Court decide to apply some form of heightened scrutiny, Section 3 would be in particular trouble (for reasons identified by the Second Circuit). But even under heightened scrutiny, Proposition 8 and other state laws refusing to recognize same-sex marriage might survive.