What is accurately gleaned by a President's religious affiliation in a country w/ separation of state & church

You can learn he's not fit to lead, whatever the beliefs or affilications. My Arab Grandpa brought me up on what he called "the lessons of the King", learned through generations of being tribal leaders. About the first rule was that a leader is a dead man because he belongs to his people - so he has nothing to lose and can act freely in their best interests. The second rule was that the king cannot afford to believe in anything at all, but must judge everything on the facts as they present themselves, and what will do the greatest good for the greatest number. The third rule was that any belief is likely to be an illusion - and illusions persisted with can become delusions which are like mirages in the desert - misleading and dangerous. Most modern so-called "leaders" lack such training, and that's largely why we're in the trouble we're in. The other part of the problem is those who follow them. Ultimately, we all carry the same responsibilities as "the king", and need the same training!