The Obama administration's new policy regarding the Defense of Marriage Act (DOMA) hinges on its conclusion that legal discrimination based on sexual orientation should be subject to "heightened scrutiny," a.k.a. "intermediate scrutiny." This equal protection test, which applies to discrimination based on sex, requires that disparate treatment be "substantially" related to an "important" government interest. It is more demanding than "rational basis" review, which applies to equal protection claims that don't involve suspect classifications or fundamental rights and requires only that a challenged law be "rationally related" to a "legitimate" government interest, but less demanding than "strict scrutiny," which applies to racial discrimination and requires a "close" relation to a "compelling" interest. Attorney General Eric Holder says DOMA, which bars the federal government from recognizing marriages between people of the same sex, cannot survive heightened scrutiny. If so, it is hard to see how state bans on gay marriage can be constitutional. Yet President Obama is still officially against gay marriage, although he says his views are "evolving."
It is possible to oppose DOMA on 10th Amendment grounds (since it favors some state marriage laws over others) without supporting the legalization of gay marriage. But if DOMA violates the right to equal protection because its distinction between gay and straight marriages is not substantially related to an important government interest, how can states draw the same distinction without violating the same right?