Isn't that pretty much the way it already is, what with the various "Christian Identity" splinter groups covering one end, and the National Council of Churches (or whatever its name is) covering the other?
There's a certain amount of that, of course, but (1) The denominations tend to break along theologically liberal or conservative lines rather than politically liberal or conservative (granted that often theological liberals and political liberals often go together as do theological and political conservatives, though the correlation is very far from perfect); and (2) the "Christian Identity" groups and the "National Council of Churches" aren't primarily political entities.