At American Creation, Tom Van Dyke has a post that features a letter of WILLIAM E. CHANNING, Minister of the Church of Christ in Federal Street, Boston (one of the most notable American Unitarians of that era) to TO THE REV. SAMUEL C. THACHER, circa 1815.
The perennial question is whether "unitarianism" (the name of the theology) or "Unitarianism" (the name of the Churches) qualifies as "Christianity" as it claimed it did.
From Rev. Channing's letter, what it isn't:
"I fear, that the Author of the Lord's prayer will, according to this rule, be driven as a heretick from the very church which he has purchased with his own blood. In that well known prayer I can discover no reference to the "inspiration of the holy scriptures, to the supreme divinity of the Son and Holy Ghost, to the atonement and intercession of Jesus Christ, to the native and total depravity of the unregenerate, and to the reality and necessity of special divine grace to renew and sanctify the souls of men;" and these, let it be remembered, are _five_ out of the _six_ articles which are given by the Reviewer as fundamental articles of a christian's faith."
And what it is:
"The word UNITARIANISM, as denoting this opposition to Trinitarianism, undoubtedly expresses the character of a considerable part of the ministers of this town and its vicinity, and the commonwealth...We both agreed in our late conference, that a majority of our brethren believe, that Jesus Christ is more than man, that he existed before the world, that he literally came from heaven to save our race, that he sustains other offices than those of a teacher and witness to the truth, and that he still acts for our benefit, and is our intercessor with the Father. This we agreed to be the prevalent sentiment of our brethren."
To many of the "orthodox" of today and back then, unitarianism is not "Christianity" whatever it calls itself. Ironic in that many/most "Christian Nationalists" are orthodox Christians who likely would term non-Trinitarianism as "not Christian."
But if unitarians are "Christians" then that captures a lot more notable Founders (Jefferson, J. Adams, Franklin, probably Madison, and contemporaries of Channing, Joseph Story and Jared Sparks) as "Christians."
That would bring us closer to a "Christian" Founding.
Here Thomas Jefferson writes to Timothy Pickering (February 27, 1821) commenting on one of Rev. Channing's sermons:
I thank you for Mr. Channing's discourse, which you have been so kind as to forward me. It is not yet at hand, but is doubtless on its way. I had received it through another channel, and read it with high satisfaction. No one sees with greater pleasure than myself the progress of reason in its advances towards rational Christianity. When we shall have done away the incomprehensible jargon of the Trinitarian arithmetic, that three are one, and one is three; when we shall have knocked down the artificial scaffolding, reared to mask from view the simple structure of Jesus; when, in short, we shall have unlearned everything which has been taught since His day, and got back to the pure and simple doctrines He inculcated, we shall then be truly and worthily His disciples; and my opinion is that if nothing had ever been added to what flowed purely from His lips, the whole world would at this day have been Christian. I know that the case you cite, of Dr. Drake, has been a common one. The religion-builders have so distorted and deformed the doctrines of Jesus, so muffled them in mysticisms, fancies and falsehoods, have caricatured them into forms so monstrous and inconceivable, as to shock reasonable thinkers, to revolt them against the whole, and drive them rashly to pronounce its Founder an impostor. Had there never been a commentator, there never would have been an infidel. In the present advance of truth, which we both approve, I do not know that you and I may think alike on all points. As the Creator has made no two faces alike, so no two minds, and probably no two creeds. We well know that among Unitarians themselves there are strong shades of difference, as between Doctors Price and Priestley, for example. So there may be peculiarities in your creed and in mine. They are honestly formed without doubt. I do not wish to trouble the world with mine, nor to be troubled for them. These accounts are to be settled only with Him who made us; and to Him we leave it, with charity for all others, of whom, also, He is the only rightful and competent Judge. I have little doubt that the whole of our country will soon be rallied to the unity of the Creator, and, I hope, to the pure doctrines of Jesus also.