A reader makes a good point about focusing too much on the demographic results of S.C.:

I think focusing on the racial breakdown of the vote only plays further into the Clinton camp's hands in terms of how they are trying to redefine the election — no matter that the immediate data seems to refute their claim, it still changes the conversation from one about the future of this country to one about race, something Obama has tried hard to transcend at every step.  Let's focus instead on the fact that, in a hard-fought, three way race, he pulled what looks like a clear majority of the votes, with a 25+ point margin over Clinton.  That's a decisive victory no matter what way you slice it.