Particularly in the US where the two-party system really makes the real extreme wings powerless, with the two major parties really relatively close together in terms of ideas and policy, at least if you compare their "average" members of Congress (on the regional and local levels, they're not necessarily further apart in any given location, but NYC Republicans will be further left in some regards than red state rural Democrats, obviously, so the gap between the most liberal regional/local Dem politician in the entire country and the most conservative Republican one does become rather large).