Publius succinctly describes what Obama could do to racial politics:
As of now, coded racism (from Nixon to Bush 41) has been a politically rational strategy at the presidential level. (Bush 43 has, to his credit, avoided it). The Willie Horton ad was disgraceful, but it was also successful. In the Darwinian world of politics, it was effective strategy.
An Obama victory would change this racial calculus completely. It would be a true watershed in that it would signal to future campaigns that a new national political majority has emerged that not only rejects race-baiting, but that (more crucially) doesn't depend upon the votes of those swayed by race-baiting.
For this reason, there's more at stake in this election than the substantive reforms Obama (and Clinton) have discussed. The 2008 election also offers a chance to exorcise some of the demons of history. Call it identity politics if you will, but I think it would be enormously significant - and beneficial - for a nation of former slaveholders to elect its first black president. Would it make the past go away? Of course not. But it would represent both substantive and symbolic progress on addressing America's original sin.