"In Scotland and Ireland, one's religion is widely used to define one's political beliefs....I fear that is also starting to happen in the US."

I don't think that statement would stand up to any real kind of scrutiny as far as Scotland is concerned. Certainly not in the Scotland of the second half of the 20thC and 21stC. Yes Labour used to get a fair percentage of the Catholic vote but that probably had as mush to do with where much of that population was located as it had to do with actual religion. Catholics don't really vote on block on a religious basis and Protestants (who make up the vast bulk of the population) certainly don't.