Government agencies have been advised to enforce the law until Congress repeals it. As a result, Obama's decision alone will likely have very little impact on same-sex couples who feel like second-class citizens because they can't get spousal benefits.
Signed by President Bill Clinton, the law defines marriage as only between a man and a woman and bans the federal government from recognizing a same-sex marriage even if it occurred in one of the five states, or District of Columbia, where it is legal.
DOMA denies federal benefits granted to other married couples, such as health insurance, Social Security survivor payments, and the right to file joint tax returns.
The president's new position is a reflection of his past awkwardness on this issue. While proclaiming during his election campaign that he believes marriage was meant to be between a man and a woman, Obama also said he opposed the marriage law.
The administration's retreat from defending the law should give a boost to cases opposing the federal statute in Massachusetts, New York, and Connecticut. In fact, it was filing deadlines in those cases that forced the administration to decide whether to continue to defend the law.
In distancing the administration from the marriage law, Attorney General Eric Holder made a solid argument that gays and lesbians deserve the same equal-protection rights granted to other groups to counter discrimination.
That argument was also at the crux of the repeal of the military's "don't ask, don't tell policy," which kept homosexuals from openly serving their country.
But changing America's concept of marriage will be harder. Gay marriage has been rejected in all 31 states where it has appeared on a referendum ballot. Obama has taken another step to change attitudes, but it is a small step.