The 9th Circuit, by contrast, applied the "rational basis" test, the standard typically used in equal protection cases that do not involve a fundamental right or a "suspect class" such as race. Under that standard, the government need only show that the challenged law "bears a rational relation to a legitimate end."
The appeals court concluded that Proposition 8, a 2008 ballot initiative that amended the state constitution to reverse a California Supreme Court decision allowing gay couples to marry, failed even this highly deferential test because it did not accomplish anything that was plausibly related to its ostensible goals.
Under California's "domestic partnership" law, gay couples retain the same rights as straight couples, except for the right to call their relationship a marriage. Since Proposition 8's sole effect was to remove that label, the court reasoned, its only justification was to mark gay marriages as morally inferior -- an illegitimate end under the Equal Protection Clause.
This analysis is unlikely to apply elsewhere because California's combination of a strong domestic partnership law with a constitutional amendment rescinding gay marriage rights is unusual, if not unique. But many other states' gay marriage bans could be vulnerable under the heightened scrutiny that Obama applied to DOMA.
Obama may wish to avoid the implications of his constitutional logic until after the presidential election. But if the Supreme Court agrees to hear the California case this fall and asks the solicitor general to weigh in, that may not be possible.