The Obama administration announced Wednesday that the Justice Department would quit defending, for legal reasons, the Defense of Marriage Act of 1996. Just two years ago, this would have ignited a fiery political backlash. But the response from Republicans about the decision to quit contesting states' measures to allow same-sex marriages can be described as tepid, at most. The difference suggests a cultural shift and broadening acceptance of gay marriage, at least as a constitutionally protected personal decision, that is striking and far reaching.

Though President Obama himself has long favored civil unions over marriage status for same-sex couples, the Justice Department apparently was forced to consider the constitutional grounds against the 1996 federal law banning same-sex marriage as it prepared to defend the law in two pending lawsuits in federal district courts.

One lawsuit, for example, involved a claim by an 81-year-old widow, Edith Windsor, for return of $360,000 in estate taxes that she had been forced to pay because the federal government, under the 1996 act, did not recognize her Canadian marriage to her deceased same-sex spouse. The New York district court is in a circuit that had no precedent case, as in other circuits, to support a ruling that prior law allowed it to exempt a charge of undue discrimination against gay couples. Thus, Justice Department attorneys reportedly concluded that they could not successfully argue the constitutional grounds for discriminatory treatment against gay couples with respect to the plaintiff's estate taxes, which she would not have had to pay had her marriage been to a man.

Justice Department lawyers would have had to file a response to the two lawsuits contesting the Defense of Marriage Act by March 11. According to a New York Times report on the cases, the Justice Department lawyers decided that a strategy of continuing to defend the constitutionality of a law that specifically fostered defense of unconstitutional discrimination would have been "legally and politically" unsustainable if they had had to argue that gay citizens had not been "historically stigmatized and can change their orientation."

The legal logic for the shift by the Justice Department is sound and virtually unarguable. Given the voluminous medical research into the genetic basis for sexual orientation and the undeniable historical record of discrimination against homosexuals, it is impossible to imagine nowadays that a court could sanction a level of official discrimination that would sustain a constitutionally sound basis favoring legal prejudice against same-sex marriages.

Gay advocates have worked for years to introduce the constitutional flaws involved in federal and state laws prohibiting gay marriage, and the two cases that brought the issue to a head could well prove to be the anchor for their argument to dismantle all state laws against same-sex marriage.

Beyond that, these cases may serve to undo strictures in employment, spousal benefits, adoption and immigration that are admittedly prejudiced against gay and lesbian marriages. Though that would not prevent churches and their congregations from setting their own religious standards for church-sanctioned marriages, the Justice Department's decision could well begin the unraveling of state civil laws that ban same-sex marriage and support disparate treatment for gay couples.

The irony here is that the federal Defense of Marriage Act, passed by Congress mainly in response to the gay rights movement, has become the legal and political vehicle that may now serve as the basis for eliminating constitutional prejudice against same-sex marriage, the penultimate goal of gay rights advocates.

Republican leaders' tepid responses to the Justice Department's announcement suggest that they themselves recognize that the law they pushed just 15 years ago as a cornerstone for their "values" agenda has become a sinking anchor. That's reflected in public opinion polls, which now largely accept gay rights, and in the stands taken in support of gay marriage by such neocon stars as former Vice President Dick Cheney and Barbara Bush, the previous president's daughter. Both are outspoken advocates of gay marriage.

In fact, the shift may mean that that gay rights, which not too long ago was conservatives' preeminent wedge issue, has at last lost its edge as a scare tactic to divide voters.