It'll be difficult to think in terms of "us" and "them" if he's elected, but more so because I think the "them" would view it as having finally arrived in "Mainstream America" (whatever that is). It's more difficult to treat blacks and other minority groups as "others" when the president is a popular black guy with what most Americans will likely hear as a very African- and kind of Islamic-sounding (especially if you add in the Hussein) name. Even more so if his Veep is Bill Richardson, who's half-Latino.
It changes Americans' perspective of how they view America. "E Pluribus Unum" kind of stuff, I guess. And it potentially helps in the country's view of the world by making the country knock off the subconscious "(white) America vs Scary Brown PeopleTM" thing that I do think infects people's perspective to some degree, especially if Obama adopts a more integrated, internationalist approach compared with the past.
The danger, of course, would be that issues primarily affecting poor kids from non-white backgrounds might be ignored by whites even more, because "We elected a black president." It could be more difficult to shine a light on racial and ethnic inequality, which is why electing him has to be backed by substantial changes in domestic policy. WHEEEEEEEEEEEEEEEEEEEEE!
It's a friggin' vicious circle of deprivation, isn't it? When the capital development of a country becomes a by-product of the activities of a casino, the job is likely to be ill-done. — John M. Keynes