Christianity never became monotheistic. It always was.
Its founding was based on there being only one God, not many.
I don't think everyone does what I was describing. Right wingers do not typically scoff at religion or the Bible.
More democrats and liberals tend to scoff at religion and will use, exploit, or take advantage of the Bible when it aligns with their liberal agenda.
One day its "God is a wizard living in the sky" the next day it's "God says thou shall love thy neighbor, and that would include gays".
Or the famous "Jesus was a liberal" because of this, that or the other.
But that's not to imply that there are no right wing bible thumping hypocrites.