CS Lewis noted that we do not have the option of having no doctrine or no dogma. If we do not have good theology, we will not have none, we will have bad theology.
When I became a born-again evangelical Christian among the Jesus freaks in the late 70's, there was a dominant political idea that America had always been a Christian nation, however imperfectly, and chosen for some special task in the world. There was a wide variety of belief along these lines, but it was generally characterised by 1) noting the deep Christian faith of some of the colonists and founders, and their intentionality in applying Biblical principles to government, 2) application of God's promises to Israel as applicable to any modern nation which chose to embrace them, meaning basically America, and 3) the reflection of this, that God might cease to protect a nation which did not follow His laws.
Even without having studied this, I was suspicious, and grew to dislike it more as the years passed. I got pretty tired of hearing the verse "If my people, who are called according to my name..." Nonetheless, I learned a lot from it. Of the two competing America as Savior/America as Oppressor myths that continue to dominate our discussions, I had moved to the Oppressor Lite viewpoint as far back as 8th grade, which only intensified through highschool and college (though W&M was a fairly nonpolitical school then). Finding that American exceptionalism, even if some folks exaggerated it, had some powerful evidence behind it, and was not merely a lie told to elementary school students, was a wonderful counterweight to the tired cynicism of the humanities and college popular culture.* Compared to everyone else, America had indeed done some remarkable things, which the rest of the Anglosphere imitated shortly.
Still, there was something deeply wrong general premise. I generally just let it slide with most folks, but among those I thought could hear it, I leaned in a bit. It was a bit of a balancing act, because there was always plenty of clergy and reflexive liberals of the laity in the mainstream who had come under the Oppressor Lite spell and needed to be leaned against in the other direction. Especially tough when you've got some of each in the audience. Yet in both cases, I always thought of it as an extra. Politics was important in that it is the acting out of our faith on a societal level, but really, when you push it, Jesus didn't talk about it much, nor did Peter, Paul, John, Luke, or James. The expansion of Christian principles into ruling and governing principles came later - into towns and districts in the 3rd C, then nations and empires in the 4th.
It was not ever thus in America. The idea of New Eden and special dispensation in the New World had been present since the beginning, but it was never universal, and it was quite uncommon among evangelicals and fundamentalists from 1900 until 1970 or so. America was considered a nice place with religious freedom, but ultimately just as much a part of the worldly world as the lands left behind. There are still denominations, especially heterodox ones, which teach that. Only recently - perhaps as a countermovement to the Protestant clergy deciding quietly in the 1920's and 30's, then noisily in the 1960's, that Jesus was really about socialism - did an evangelical American exceptionalist bloc develop.
I treated it as a small thing, but now it is bearing bitter fruit. Good, decent people are insisting that God is calling them to take a stand to make America reflect Christian values, believing they must not take photographs or bake cakes for gay weddings, or refusing to issue marriage licenses for same. Their courage is greater than mine, and they believe they are protecting even those who vilify them by their actions. I pray that their reward in heaven is great, even as God smiles and says "that was not where your energy should have gone." Even as I think them wrong, I see that I am not quite worthy to even mention it to them.
But the theology is wrong. There is not good scriptural evidence that God offers this Chosen People deal to any nation, perhaps not even Israel anymore. The Church, the Christian community is the new tribe, and nations are merely a way that we organise things for ourselves.
*That album was actually a watershed event for me. Just hearing the title caused me to suspect that I gotten to some ridiculous exaggerated point. The gradual rising of Tolkien, Lewis, and the Arthurian legends in my dual, non-integrated outlook seemed increasingly sensible.