Just because the Right Christians make up 75% of the republican party does not mean there is no separation between church and state. The fact that there is just a simple majority of Republicans in congress right now shows that the right siders do not have control of anything.
The percentage of Christians in each group might also be more of a reflection of personal beliefs matching the beliefs of the party.
Such as people who hate the idea of legalizing marijuana are more likely to be leaning to the conservative parties where those who want to go topless and have more nude beaches are going to vote or work for a liberal based party.