Halle Berry was lauded as "the first black actress to win a Best Actress Oscar." Halle Berry's mother was white (and English!) and her father was black.
Playwright August Wilson wrote a very famous ten-play cycle chronicling the African-American experience in the 20th Century. He was regarded as the nation's foremost black playwright. Wilson's father was white (and German!) and his mother was black.
I know of no media outlet that has EVER criticized the Academy-Award-winning Berry or the Pulitzer-prize-winning Wilson for characterizing themselves as "black." When Berry wept onstage at the 2002 Academy Awards, saying it was a "historic moment," where were the pundits screaming, "she's not REALLY black! It's only HALF-historic!" When Wilson died recently and was lionized as a hero of African-Americans everywhere, where were the bloggers shouting, "he wasn't REALLY black! He's only a PARTIAL hero!"
Face it: the people who are trying to imply (or flat-out say) that Obama, as an American of African descent, should be self-identifying as "biracial" or "multiracial" are close-minded bigots. Who cares how he characterizes himself? What right do we have to look at another human being and say, "He must call himself this or that or the other thing!" I can think of a few other cultures that have gone this route: one is Rwanda. They forced people to identify themselves on their government ID cards as Hutus or Tutsis (even if they were both). Then the Hutu government sanctioned genocide of the Tutsis. There was another group, a while back, that actually forced people to wear patches and tattoos to identify their ethnic status, no matter what the people wanted to be identified as (they were small patches and tattoos...stars of David and such).
As long as he identifies himself as an American and a progressive, that's enough for me. I don't care if our next President is black, white, brown, gray, blue, or polka-dotted. As long as his (or her) policies are sound and he (or she) is democratically elected, that's enough for me.