Here is a newish article by Wallbuilders entitled: The Founding Fathers on Jesus, Christianity and the Bible. The first person David Barton turns to for evidence is John Adams, the second President of the United States. The quotations Barton reproduces follow:
The general principles on which the fathers achieved independence were the general principles of Christianity. I will avow that I then believed, and now believe, that those general principles of Christianity are as eternal and immutable as the existence and attributes of God.1
The Holy Ghost carries on the whole Christian system in this earth. Not a baptism, not a marriage, not a sacrament can be administered but by the Holy Ghost. . . . There is no authority, civil or religious – there can be no legitimate government but what is administered by this Holy Ghost. There can be no salvation without it. All without it is rebellion and perdition, or in more orthodox words damnation.2
Without religion, this world would be something not fit to be mentioned in polite company: I mean hell.3
The Christian religion is, above all the religions that ever prevailed or existed in ancient or modern times, the religion of wisdom, virtue, equity and humanity.4
Suppose a nation in some distant region should take the Bible for their only law book and every member should regulate his conduct by the precepts there exhibited. . . . What a Eutopia – what a Paradise would this region be!5
I have examined all religions, and the result is that the Bible is the best book in the world.6
Okay, taken at face value, many an evangelical, the Bible is the infallible Word of God, type would think "John Adams was one of us." What Barton doesn't tell us is for his entire adult life Adams identified as a Unitarian. Adams rejected original sin, the Trinity, Incarnation, Atonement and eternal damnation sometimes bitterly and mockingly so. And towards the end of his life Adams got even more heterodox, elevating man's reason so far over revelation that he noted if God Himself revealed the doctrine of the Trinity to him with Moses on Mt. Sinai, he still wouldn't believe it because man's reason proves 1+1+1 = 3 not 1. And asserting exotic world religions like Hinduism and Zeus worship teach "Christian principles."
That's why you have to examine the WHOLE of what a Founder believed, not cherry picked selected quotes, taken out of context which mislead. This kind of clarification is utterly absent from Barton's presentation of the evidence.