Flyover Nation sounds a note of caution about linking the church too closely with politics. I have never liked the idea of the church being simply the Republican party at prayer. In the UK it was always the Tory party/conservatives who were seen to be intrinsically linked to church.
I agree Christians shouldnt be partisan, but at the same time we should be involved in the important issues.
A Christian pastor is OK to highlight where various candidates stand on certain issues. But he should not say to his congregation “to be a Christian you must vote for this candidate” either in word or by implication.
Using churches as political campaign tools sullys the name of Christ in my view.