Obama so far has a majority among black and younger voters also he is popular with regular churchgoers. Clinton is the candidate for the older black community, the retired population and female voters. Also, and very interestingly, Clinton is the candidate for those with knowledge about the issues and the economy; in contrast Obama is more likely to attract the disillusioned and apathetic who seek change but find it harder to articulate their desires. Perhaps that is why his campaign relies on rhetorical cues and he avoids issues and policy; or is it that only those who do not really think carefully about policy and issues will follow his style of campaigning.
I think a serious problem he will face is his lack of experience and lack of substance; while he can deliver great oratory can he be trusted to deliver great government? That’s the decision US Democrats face and perhaps the segmentation that is emerging reflects how the campaign styles are playing out with voters. For more data and details see: http://news.bbc.co.uk/1/hi/world/americas/7211535.stm