Herman Cain has been unironically arguing that "[o]ur Constitution guarantees the separation of church and state," in support of discriminating against American Muslims, but Nick Sementelli points out that he wasn't always such a fan of the concept, at least not in 2006:
Too many Americans are guided and implicitly threatened by the misinterpretations of the Constitution's establishment clause that found a non-existent "separation of church and state."
So to reiterate: Herman Cain believes "separation of church and state" is a "misinterpretation of the Constitution." Unless Muslims are involved, in which case that separation is ironclad and means mosques can be banned.
*post edited for clarity