Democrats were hoping to use gay marriage as a "wedge" issue against Republicans
No doubt support for gay marriage is assumed in the liberal heartland of the "sophisticated" urban and metropolitan areas on the coasts. In the rest of the country, however, the idea is far less extensively embraced.
And rather than serving as a "wedge" issue for Democrats against Republicans, the truth is that the controversy divides important parts of the Democrat coalition -- socially liberal young people vs. more socially conservative African Americans and members of the white working class. The President -- and Democrats generally -- need both to win.
No doubt the President could come out and support gay marriage without significant erosion of the African American vote. But the damage this issue (and its continued prominence in the news) does to Democrats may be more at the statewide-race level, for example in races for US Senate seats. For example, what does Virginia's Tim Kaine think about gay marriage?
Perhaps the Obama campaign needs to look for a new bright, shiny object to use to try to distract voters from the state of the economy.