Joe Carter have a
very good piece here responding to arguments about evangelical over-engagement in politics. Here's the heart of the matter:
Rather than assuming that evangelicals are a large, powerful, committed political bloc that, for some inexplicable reason, is completely ineffective, the more realistic conclusion is that politically engaged evangelicals are like a herd of unicorns: powerful and abundant in the imagination while not actually existing in the real world.
Read the whole thing (and this time I mean it).