Before anyone can talk about what's "American" and what's not, it's first necessary to define what being "American" means.
It can be purely geographic, but that doesn't really distinguish much. One might as well say that he's an Ohioan, as it would be more specific.
Almost everyone will argue that he/she loves "America," but what is it that is loved? The physical space he/she occupies? The physical comforts? The money? The freedom to move from point A to point B? Any of those can be had in France or Germany or England.
America is distinguished by its founding document, the Constitution, a political document unlike any other in the world. The freedoms ensured in the Constitution and the limitations on government imposed by it are what make America unique.
Therefore, to be un-American is to violate the Constitution, or desire to twist its words to mean what they do not, to use it for means that it was never intended. There have been and are now plenty of people willing and trying to remake the Constitution to suit their ends, and those people are in both parties, and those people are un-American.