How is political ideology used to define who is and who isn't American?

I would argue that we define who is and is not American,
at least in some ways, by the political ideology that people hold.  This is a much more
important determinant of who is and is not an American than anything like race or
class.  We believe that Americans have to believe in republicanism (which is more or
less another term for democracy).

This can be seen most
clearly when you look at the sorts of political ideologies that are abhorrent to
Americans.  Many, if not most, people would argue that a socialist or communist cannot
be an American because those ideologies are antithetical to American republican values. 
The same would go for someone who was a monarchist.

We in
the US define ourselves by our belief in democracy.  People who are not committed to
that set of values are not typically seen as authentic
Americans.