That’s what Diaz v. Brewer looks like to me, though the case approaches the question indirectly. Here’s a brief summary:
1. Arizona used to provide health-care benefits for spouses of state employees (as well as dependent children, but that’s not relevant here). In April 2008 an administrative regulation expanded this to include domestic partners, both opposite-sex and same-sex. But in September 2009, the state Legislature enacted a statute that limited such benefits to spouses plus dependent children, and thus excluded domestic partners.
2. Gay and lesbian employees sued, claiming this violated the Equal Protection Clause. A district court agreed, and issued a preliminary injunction barring enforcement of the new statute. “While the district court noted that Section O was not discriminatory on its face, because it affected both same-sex and different-sex couples, the court held that Section O had a discriminatory effect. This is because, under Arizona law, different-sex couples could retain their health coverage by marrying, but same-sex couples could not.”
3. The Ninth Circuit affirmed, concluding that the law violated the Equal Protection Clause, because it isn’t rationally related to a legitimate government interest (the so-called “rational basis” test). The court did not simply say, as it might have when reviewing a preliminary injunction, that the plaintiffs had merely shown a likelihood of success on the merits:
[T]he district court correctly recognized that barring the state of Arizona from discriminating against same-sex couples in its distribution of employee health benefits does not constitute the recognition of a new constitutional right to such benefits. Rather, it is consistent with long standing equal protection jurisprudence holding that “some objectives, such as ‘a bare ... desire to harm a politically unpopular group,’ are not legitimate state interests.” Moreover, the district court properly rejected the state’s claimed legislative justification because the record established that the statute was not rationally related to furthering such interests.
So the logic is that limiting benefits to spouses is unconstitutional, because it in effect constitutes discrimination against same-sex couples, because (as the Ninth Circuit earleir stated) “same-sex couples in Arizona are prevented [from marrying] by operation of law.” And the Circuit said that “the district court properly concluded that the denial of benefits to same-sex domestic partners cannot promote marriage, since such partners are ineligible to marry.”
It’s possible to distinguish laws limiting marriage to opposite-sex couples from laws limiting benefits to opposite-sex married couples; perhaps the Circuit would eventually conclude that there is a sufficiently rational basis for so limiting marriage, even though it has concluded that there is no such basis for so limiting benefits. But it seems to me that the similarities of the cases are likely to be more influential to future panels than the differences.
I thus expect that the Diaz decision to play an important role in any future Ninth Circuit decision on Proposition 8, at least unless either Diaz or the Proposition 8 case goes en banc, or the U.S. Supreme Court agrees to hear the Diaz case, which is unlikely but possible. (I assume here that the California Supreme Court instructs the Ninth Circuit that the intervenors in the Ninth Circuit case have standing, so that the Ninth Circuit case won’t be thrown out on procedural grounds.) Thanks to How Appealing for the pointer.
UPDATE: Ed Whelan (National Review Online) criticizes the ruling.