Since we are on the topic of Mormonism at American Creation, I believe the LDS make a good "test case" for the "Christianity" of the American Founders (or that of the so called "key Founders"). The Mormons consider themselves "Christian." So did (or likely did) Washington, J. Adams, Jefferson, Madison, Franklin, G. Morris, Hamilton, and some others. Both groups certainly operate in the larger tradition of "Judeo-Christian" Providentialism. Yet, the "orthodox" generally don't consider "Mormonism" to be "Christianity." If Mormonism can't pass the "Christianity" test of the "orthodox," neither could the religion of each above mentioned Founding Father with the exception of, perhaps, Hamilton at his deathbed.
Moreover, Mormonism, because it was formed post-American Founding, more authentically incorporates "American theology" than historic Christianity does. Historic Christianity believes revelation stopped some 2000 years ago. Some of the adherents of the "Christian America" crowd act as though the American Founding was a "divine" event, the founding documents, "divinely inspired." Viewing the founding documents as divinely inspired is blasphemy to orthodox Christianity, properly understood. But it is, or could be, legitimately part of Mormonism.
Indeed, as far as I know, some of the eccetric beliefs of the Mormons that do not derive from orthodox Christianity actually trace back to the American Founding Fathers. Notions like God is a Being of material matter which Joseph Priestley and Thomas Jefferson (and John Locke?) believed. Or the idea that American Indians may be part of the "Lost Tribes of Israel," which, among others, the orthodox figure Elias Boudinot posited.
Here is Ben Franklin flirting with a theology that might aptly be termed "proto-Mormonism." (I wouldn't at all be surprised if the following sentiment influenced the Founders of Mormonism). As he wrote in 1728:
I believe there is one Supreme most perfect Being, Author and Father of the Gods themselves.
For I believe that Man is not the most perfect Being but One, rather that as there are many Degrees of Beings his Inferiors, so there are many Degrees of Beings superior to him.
Also, when I stretch my Imagination thro' and beyond our System of Planets, beyond the visible fix'd Stars themselves, into that Space that is every Way infinite, and conceive it fill'd with Suns like ours, each with a Chorus of Worlds for ever moving round him, then this little Ball on which we move, seems, even in my narrow Imagination, to be almost Nothing, and my self less than nothing, and of no sort of Consequence.
When I think thus, I imagine it great Vanity in me to suppose, that the Supremely Perfect, does in the least regard such an inconsiderable Nothing as Man. More especially, since it is impossible for me to have any positive clear Idea of that which is infinite and incomprehensible, I cannot conceive otherwise, than that He, the Infinite Father, expects or requires no Worship or Praise from us, but that he is even INFINITELY ABOVE IT.
But since there is in all Men something like a natural Principle which enclines them to DEVOTION or the Worship of some unseen Power;
And since Men are endued with Reason superior to all other Animals that we are in our World acquainted with;
Therefore I think it seems required of me, and my Duty, as a Man, to pay Divine Regards to SOMETHING.
I CONCEIVE then, that the INFINITE has created many Beings or Gods, vastly superior to Man, who can better conceive his Perfections than we, and return him a more rational and glorious Praise. As among Men, the Praise of the Ignorant or of Children, is not regarded by the ingenious Painter or Architect, who is rather honour'd and pleas'd with the Approbation of Wise men and Artists.
It may be that these created Gods, are immortal, or it may be that after many Ages, they are changed, and Others supply their Places.
Howbeit, I conceive that each of these is exceeding wise, and good, and very powerful; and that Each has made for himself, one glorious Sun, attended with a beautiful and admirable System of Planets.
It is that particular wise and good God, who is the Author and Owner of our System, that I propose for the Object of my Praise and Adoration.
Now, the above sentiment was one of Franklin's personal theological eccentricities probably not shared by the other key Founders. And indeed I don't think that the key Founding Fathers would endorse many of the eccentricities of Mormonism. I also believe that the key Founders' theology is far more rationalistic and enlightenment oriented than is Mormonism. However, I am certain that the key Founders would have accepted Mormons' proper place at the table of American civil religion along with the Trinitarians and everyone else who believed in Providence and a future state of rewards and punishments. Remember, the test of "true religion" for men like Washington, J. Adams, Jefferson and Franklin was that it in fact produced virtue. And, according to the standards of so called "traditional Judeo-Christian morality," Mormons tend to live more "moral" lives than orthodox Christians. Hence Mormons, because they tend to be more "virtuous" than the orthodox would be saved BEFORE the orthodox, (if I dare assert what Washington et al. probably would have believed were they to witness Mormonism).
The key Founders probably would have viewed the Mormons' eccentric teachings not unlike they did the Swedenborg's. Here is what Wiki informs on that Church:
Swedenborg explicitly rejected the common explanation of the Trinity as a Trinity of Persons, which he said was not taught in the early Christian Church. Instead he explained in his theological writings how the Divine Trinity exists in One Person, in One God, the Lord Jesus Christ. Swedenborg also rejected the Protestant doctrine of salvation through faith alone, since he considered both faith and charity necessary for salvation, not one without the other. The purpose of faith, according to Swedenborg, is to lead a person to a life according to the truths of faith, which is charity.
At the age of fifty-six he entered into a spiritual phase, in which he experienced dreams and visions. This culminated in a spiritual awakening, where he claimed he was appointed by the Lord to write a heavenly doctrine to reform Christianity. He claimed that the Lord had opened his eyes, so that from then on he could freely visit heaven and hell, and talk with angels, demons, and other spirits. For the remaining 28 years of his life, he wrote and published 18 theological works, of which the best known was Heaven and Hell (1758) , and several unpublished theological works.
In other words, a non-Trinitarian Church with a famous leader who, apparently, believed in additional revelation from Angels to further "reform" Christianity.
And here is how Washington dealt with them:
To the members of the New Church at Baltimore.
It has ever been my pride to mind the approbation of my fellow citizens by a faithful and honest discharge of the duties annexed to those Stations to which they have pledged to place me; and the dearest rewards of my Services have been those testimonies of esteem and confidence with which they have honored me. But to the manifest interpretation of an over-ruling Providence, and to the patriotic exertions of United America, are to be ascribed those events which have given us a respectable rank among the nations of the earth. --
We have abundant reason to rejoice that in this land the light of truth and reason has triumphed over the power of bigotry and superstition and that every person may here worship God according to the dictates of his own heart. In this enlightened Age & in this Land of equal liberty it is our boast, that a man's religious tenets, will not forfeit his protection of the Laws, nor deprive him of the right of attaining & holding the highest offices that are known in the United States.
Your Prayers for my present and future felicity were received with gratitude; and I sincerely wish, Gentlemen, that you may in your social and individual capacities, taste those blessings which a gracious God bestows upon the Righteous.
Again, as noted, Washington and company didn't endorse the eccentric teachings of Swedenborgianism and Franklin's belief in a created personal God who "owns" our solar system seemed a personal eccentric belief of his. However, the key Founders ALSO didn't endorse orthodox Trinitarian doctrine, and vacillated between scoffing at it and mocking it (Jefferson and J. Adams) and being utterly unconcerned or agnostic about it (Franklin, Washington and Madison).
As Franklin put it to Ezra Stiles:
As to Jesus of Nazareth, my Opinion of whom you particularly desire, I think the System of Morals and his Religion as he left them to us, the best the World ever saw, or is likely to see; but I apprehend it has received various corrupting Changes, and I have with most of the present Dissenters in England, some Doubts as to his Divinity: tho' it is a Question I do not dogmatise upon, having never studied it, and think it needless to busy myself with it now, when I expect soon an Opportunity of knowing the Truth with less Trouble. I see no harm however in its being believed, if that Belief has the good Consequence as probably it has, of making his Doctrines more respected and better observed, especially as I do not perceive that the Supreme takes it amiss, by distinguishing the Believers, in his Government of the World, with any particular Marks of his Displeasure.
In that letter Franklin also outlined the contents of American civil religion:
Here is my Creed: I believe in one God, Creator of the Universe. That He governs it by his Providence. That he ought to be worshipped. That the most acceptable Service we can render to him, is doing Good to his other Children.
Period. That's it. Doctrines like original sin, the trinity, the incarnation, the atonement, eternal damnation, the eccentricities of Swedenborgianism (or today what we might term the eccentricities of Mormonism) are cast off as unimportant doctrines. Or as Jefferson put it:
Every religion consists of moral precepts, and of dogmas. In the first they all agree. All forbid us to murder, steal, plunder, bear false witness &ca. and these are the articles necessary for the preservation of order, justice, and happiness in society....We see good men in all religions, and as many in one as another. It is then a matter of principle with me to avoid disturbing the tranquility of others by the expression of any opinion on the [unimportant points] innocent questions on which we schismatize, and think it enough to hold fast to those moral precepts which are of the essence of Christianity, and of all other religions.
– Thomas Jefferson to James Fishback, Sept. 27, 1809
Again the key Founders put orthodox doctrines like the Trinity and infallibility of the Bible in the same "box" as the eccentric teachings of groups like the Swedenborgs -- "unimportant points" or "innocent questions on which we schismatize" that are NOT FOUNDATIONAL to the American civil-religious order.