We're so close to a Homer Stokes style "these boys ain't white" meltdown it'd be funny if not for the seemingly gigantic contingent of racist nut cases.
Some of them seem to bring it up aggressively, claiming that Obama is pretending to be black as part of his elaborate charade, and because he's not black, Democrats can't like him any more.
After all its not like he's every publicly acknowledged his mixed background. Except that 2004 DNC speech where he introduced himself. And his books. And regularly thereafter.
"I personally believe that Obama provided a birth certificate, but let's pass legislation so that something that didn't happen can't didn't happen again!"