As Helena said, Obama was asked about this matter and his reply was ‘politically correct’ (other nations also thought of its own ‘excepcionalism’). I think the same as the USA governor, every country in the world has its good features and its bad ones, so one nation cannot be better than the rest, because they differ from several political characteristics.
From my point of view, this idea of American excepcionalism is a force for evil, because people use this ‘slogan’ to claim that their American nation is superior. America has great things, but just like any other country.