The term evangelical is too vague to be classified as a political bloc. Protestants in general are a hard bunch to classify because there are so many branch-offs and a lot of nondenominational types. Would you consider Chalcedon Presbyterian or the Missouri Synod an evangelical sect?
Theologically no, but in political terms they would probably be considered as such.
Probably the trickiest thing about this though is in urban areas there'd be a large gap between "white evangelicals" per self-description and "whites who at least semi-regularly attend an evangelical church", as people who fall into the second category but not the first would be far more Democratic than people that fall into both.