1 drop rule
The blood quantum of Barack Obama is not the question. "Not black enough" refers to the choice of ancestors. Obama's African ancestors chose the route of NOT being captured and sold as slaves, and in fact may have been the victorious tribe that managed to capture the neighboring tribesmen to be sold into slavery. These captured slaves were ultimately to be shipped to the New World, where they remained in bondage until the Emancipation Proclamation in 1863. To be "black" in America is to be able to claim descent from these slaves, and subjected to the scorn of the dominant Europeans who had occupied the North American continent. This scorn persisted, for decades after their manumission, which shaped and gave the characterization of "black".
So Obama's ancestors may in fact be the perpetrators of the involuntary servitude that befell the ancestors of the American "blacks". And they want Obama to represent them.
Stockholm Syndrome at work. The unenlightened masses still demand to remain loyal to their oppressors.
Barack Obama does business with the white overclass (repersented by the Democrat party hierarchy).
"1 drop rule"
Even though I am a blue-eyed blond, I guess that makes me an African-American, Arab-American, Native-American. Do I check them all off or go with what ever suits on any given day?