We have "smoking gun" evidence that J. Adams, Thomas Jefferson and Ben Franklin were not "orthodox Trinitarian Christians" and flunk the Athanasian test for what it means to be a mere "Christian."
There is also smoking gun evidence that a great deal of founders who tend to be more "2nd tier" were orthodox Trinitarian Christians.
My position is that the standard of scrutiny we apply in order to categorize a founder in a particular religious box is so strict that no one is entitled to a "default" position -- like "they were all Christians" (meaning to some/many "orthodox") except for a handful like Jefferson, J. Adams and Franklin and a few lesser founders who were even more "deistic" than those three (Paine, Allen, etc.).
So take someone like John Marshall, an important and notable founding founder. But not a first tier "key" Founder like the first five Presidents, Franklin and Hamilton, etc. If you knew only a surface amount about him, you'd see that like a statistical majority of the Founders, he was an Anglican-Episcopalian. So if you wanted to fill in the details about what he "really" believed, you might look to the creeds, confessions and official positions of said church and make your categorizations accordingly.
But that would be wrong. That's a lazy error that those who are sympathetic to a traditional conservative Christian founding are likely to follow. It's just as wrong as the "they were all deists" or even concluding they were all the hybrid religion (whatever we call it).
The truth is we really don't know what a particular founder believed until we do the detective work. And when we do so for Marshall, this is what we discover.
From his daughter:
The reason why he never communed was, that he was a Unitarian in opinion, though he never joined their society. He told her he believed in the truth of the Christian Revelation, but not in the divinity of Christ; therefore he could not commune in the Episcopal Church.And another quotation from U.S. Senator and former Maryland Governor William Pinkney Whyte:
He was a constant and liberal contributor to the support of the Episcopal Church.
He never doubted the fact of the Christian revelation, but he was not convinced of the fact of the divinity of Christ till late in life.
Then, after refusing privately to commune, he expressed a desire to do so publicly, and was ready and willing to do so when opportunity should be had. The circumstances of his death only forbade it ...
He was never professedly Unitarian, and he had no place in his heart for either an ancient or a modern agnosticism.And as we know, fellow Anglican/Episcopalian George Washington systematically avoided communion as well. Was it because he had a religious creed similar to Marshall's? I suspect so, but would admit, it's not a "smoking gun." It's certainly on the table of plausibility.
Finally, we can note that this creed isn't "strict deism." It believes in the Christian revelation and a special place for Jesus, even if it does not affirm Jesus' full divinity. In terms of what to call it and whether such qualifies as "Christianity" I will let others judge and decide.