As to this "USA founded on Christianity business", you need to keep in mind that the country was loosely Christian but mostly secular until McCarthyism which is when it got nutty Christian. That is when God went on the money and in the pledge.
The 60s pushed against that and so did non-christian immigrants in the force of multi-culturalism.
But God is still on the money and in the pledge and the few attempts to remove it have been overwhelmingly shouted down. The USA is more christian crazy than it was orignially intended to be.
That said, I don't really care, as I don't live there
I do care about my own nutty constitution though, which also refers to the holy (which in this case is at least mostly a relic from old brittish rule)