Politics As Usual: Why Obama Isn't Backing Gay Marriage
Josh Kraushaar speculated at TheAtlantic.com about why Obama isn't backing gay marriage -- an issue that splits his two core constituencies, college-aged voters and African-Americans:

College-aged voters are only part of the president's coalition. The bigger element consists of African-American voters, who are solidly opposed to gay marriage. California's Proposition 8 ban on same-sex marriage passed in 2008 thanks to overwhelming black support; 70 percent backed it, according to exit polls. Recent gay marriage legislation in Maryland drew opposition from leading Democratic African-American legislators in the state. The same ministers organizing get-out-the-vote efforts in black churches for Obama are also railing against gay marriage.

Obama can't afford to even risk losing the deep enthusiasm black voters have towards him. They gave Obama a whopping 95 percent of the vote against John McCain last year and turned out at historic levels. He should get similar levels of support this year, but with the down economy disproportionately affecting the black community, he's not at all assured that they'll turn out at the same level as 2008. Backing gay marriage would virtually guarantee that some would stay home -- perhaps enough to tip the balance in states like Virginia, Pennsylvania, North Carolina, and Ohio.

The conventional wisdom has been that supporting gay marriage would alienate blue-collar whites, and that's been the main reason he's been hesitant to come out in favor before the general election. But in this case, it's a crucial element of his own base that's preventing the president from taking bolder steps to advance a cause that he seems to believe in, but hasn't publicly embraced. It's as much about politics as principle.