The real surprise on Wednesday wasn't that the Obama administration decided it could no longer legally defend the federal Defense of Marriage Act, which mandates that the federal government not recognize same-sex marriages and stipulates that states need not recognize same-sex marriages from other states. It's that it took so long to get here. Recall that presidential candidate Barack Obama pledged to repeal the law, which he had called "abhorrent," in 2007. What needed to be bridged over the past two years was the distance between the president's personal views and his duty to defend a congressional statute.
That's why even as the Justice Department opted to defend the law at every legal turn, it did so claiming that "until Congress passes legislation repealing the law, the administration will continue to defend the statute when it is challenged in the justice system." As Walter Dellinger, acting solicitor general in the Clinton administration, has explained: "The government has an obligation to comply with the nation's laws, regardless of whether the president agrees with a particular statute. Doing otherwise would also set a precedent justifying similar nullifications by future administrations." The alternative, according to Dellinger, would be to have every president nullify the laws passed by his predecessors by simply declining to appeal adverse rulings.
Dellinger's proposed middle way—in the context of the October court rulings striking down the military's "Don't Ask, Don't Tell" policy—was to have the administration continue to defend the law formally in the courts while suggesting reasons the courts should strike the law down. This has happened before: The Clinton administration both enforced and argued against a discriminatory HIV policy in the military in 1996, and the law was repealed. That's precisely what the administration opted to do with DOMA on Wednesday.
Attorney General Eric Holder's letter to Congress said the Obama administration would no longer defend Section 3—and only Section 3—of DOMA in New York and Connecticut because it violates the equal-protection clause of the Fifth Amendment, as applied to same-sex couples. Last July, a federal judge in Massachusetts declared DOMA unconstitutional, because it denied federal benefits to legally married same-sex couples in the state. The Obama administration appealed that decision in January, much to the dismay of gay-marriage supporters, who argued that fighting to uphold a discriminatory law in the courts was proof of the administration's ongoing hostility to gay rights. References in government briefs to "uncles marrying nieces" weren't helping.
Section 3 provides that "in determining the meaning of any Act of Congress, or of any ruling, regulation, or interpretation of the various administrative bureaus and agencies of the United States, the word 'marriage' means only a legal union between one man and one woman as husband and wife, and the word 'spouse' refers only to a person of the opposite sex who is a husband or a wife." From now on, explained Holder, the administration will continue to enforce DOMA—but it won't defend it, because it doesn't pass the heightened standard of scrutiny it should receive in the courts.
As Adam Bonin lays it out here, bumping up the standard of review isn't mere legal semantics. In his letter, Holder explains that the administration "has defended Section 3 in jurisdictions where circuit courts have already held that classifications based on sexual orientation are subject to rational basis review, and it has advanced arguments to defend DOMA Section 3 under the binding standard that has applied in those cases." "Rational basis review" means that courts will uphold the law so long as it is rationally related to a legitimate government interest. It's the most deferential standard of review, and, Holder suggests, the administration could muster the arguments to defend it in the jurisdictions that applied that test. (Although Holder then goes on in his letter to pillory even the "rational" reasons often advanced to discriminate against gay marriage, including arguments about " 'procreational responsibility' that the department has disavowed already in litigation as unreasonable, or claims regarding the immutability of sexual orientation that we do not believe can be reconciled with more recent social science understandings.")