First of all, they arw forbidden from even endorsing a candidate. Of.clurse liberal churches do it all the time with no hear of reprisal.

No Liberals need to read the constitution. No where in there does it say "separation of church and state." There is an establishment clause and an exercise clause. 

Letting a churches have the same rights you and I have which are not based on whether not we pay taxes is fimundamental and has nothing to do with violating the establishment clause. How ever it does violate the free expression clause.