Some black Americans are convinced that Senator Barack Obama is not black or not black enough Stanley Crouch is a good example of someone holding such a view. The reasoning seems to me to be not so much that he's mixed race (which is compatible with being black) but more that he is not descended from West African slaves in the U.S. What that has to do with the concept of blackness in the U.S. is something I can't understand. Most Americans treat Barack Obama as black, and thus he is black by the operational concepts of race at work in this context. But it's certainly true that some components of what some black Americans see as crucial to their black identity are not part of his life at all (or at least not naturally; when he puts on a Southern black accent to speak at the anniversary of Bloody Sunday, that doesn't count as normally speaking that way), and being descended from West African slaves in the U.S. is one of those elements.
But now it turns out that Obama's white mother is descended from white slaveowners. It's sort of ironically funny, but what serious import does this revelation have? It's worth thinking about what significance people might find in this. The same is true of every black American descended from white slaveowners who raped their slaves, which produced mixed race offpspring who were then labeled as black. That ancestry is fairly common among black Americans today. There is one difference in this case, though. Senator Obama's maternal ancestors who were the beneficiaries of white anti-black racism (whether intentional or not) are much closer in his line than is the case with those the eventual result of slave rape. In fact, the victims of white anti-black racism are not at all in his line, at least until him, since he of course is treated as black in a society that still manifests racism. But it is the latter fact that would make him black, not the former.
Perhaps justice issues related to ancestry from slaves that some black people will have and he won't (or won't as much). But that issue is a problem for those who think certain kinds of justice are due to all black people. Trying to get around that problem by defining those who would not benefit from such proposed measures aren't really black seems to me to be illegitimate.
But this does (technically) lay to rest the claim that Senator Obama's ancestry didn't have anything to do with American slavery. For some fun video, see this Racialicious post, which contains Debra Dickerson's appearance on The Colbert Report (defending the same position as Crouch) and then a Saturday Night Live parody of Jesse Jackson and Al Sharpton discussing how black Obama is.