For several people (also in the US) someone is considered black, even if he's half white and half black.

Maybe compare it to some chancellor candidate Germany whose ancestors are half german and half turks. Several Germans would have a problem with that - for sure!

The program is idealized, no doubt.
Obama however has charisma, he has proven to be able of holding very good speeches.
His job won't be easy at all, and for sure he can't accomplish EVERYTHING. If he just helps to calm down everyhting a bit, then that's already a good thing.
We'll see.