Well, I haven't read the whole thing, but from what I have read of it, this looks to be a very good book on the founders and religion: The Faiths of the Founding Fathers, by David L. Holmes (a professor at the College of William and Mary).
In one passage, the author writes:
But if census takers trained in Christian theology had set up broad categories in 1790 labeled "Atheism," "Deism and Unitarianism," "Orthodox Protestantism," "Orthodox Roman Catholicism," and "Other," and if they had interviewed Franklin, Washington, Adams, Jefferson, Madison, and Monroe, they would undoubtedly have placed every one of these six founding fathers in some way under the category of "Deism and Unitarianism." pp 50-51.
The author apparently isn't aware of Gregg Frazer's thesis or the term "Theistic Rationalist," to describe the Founders' religious beliefs; but the facts uncovered in this book line up neatly with Frazer's argument.
And for those who believe America is a "Providential" nation, one chosen by God Himself as something *special,* who look back especially to the Founding era with sacred reverence, one has to ask why God chose to give these theological unitarians who disbelieved in eternal damnation such a *special* place in America's history as the first five Presidents and key leaders in Declaring Independence and constructing the Constitution. Perhaps, in doing so, God is sending a theological message.