AMERICAN POLITICS has been notable for its lack of ideological structure. We have had our share and more of ideological movements, but these have typically begun outside the system of political parties, thereafter seeking to influence and on occasion to penetrate the established institutions.  The latter have in the main resisted this, usually preferring to soften distinctions and to compete for votes at the center.  Accordingly, it is common for American politics to be described as pragmatic, in contrast to the complex social doctrines that guide European politics.