Well, if this is the case, then he is not half-black.
He doesn't claim to be. He passes himself off as African-American, period. No acknowledgement of his alleged mother's side of the family.
There is no way BHO is the child of Barack Sr and Kezia. They are both very African, very dark skinned.
Most African Americans, have some percentage of mixed blood that has been diluted over the generations. (Remember the old formula, anyone who was 1/16th black was listed as black, not white) BHO is less dark skinned than most African Americans because he has a higher percentage of white blood/genes, i.e., 1/2 so far as we know. Or, as some would have it, he is melanin-challenged.
And, he looks too similar to Stanley Dunham.
Nor, as is often suggested, can he be the son of Soetoro and Stanley Ann Dunham, as he is clearly part some part African, not part Asian.