I think when the founding fathers said "one nation under god," they were just acknowledging that God is the ultimate ruler ... it became something much different later.
I have no explanation for the modern era of political religiosity ..
When I was in seminary in the 90s, such things were dismissed as heresy, and even blasphemy ..
even then it was seen as somethng out there that was not real christian at all ... today its mainstream
i remember a time when one's political affiliation was not much more than your favorite baseball team -- something that didnt really matter.
i think its just another sign of the general decline of our culture..