As my estimable co-blogger Rev. Brian Tubbs defines what it means to be a "Christian":
For my own part, when it comes to assessing whether a Founder was "Christian," I believe in the KISS principle. :-) I keep it simple.
Did the person believe in Jesus Christ as his or her divine and risen Savior? (Romans 10:9-10).
That's certainly a fair biblical understanding of "Christianity." One question I have is what does "divine" mean? This isn't a stupid question. On its face, referring to Jesus as merely "divine," as opposed to "God the Son, Second Person in the Trinity" can mask differences among 1) Trinitarians, 2) Arians, 3) Mormons, 4) Jehovah's Witnesses, 5) Swedenborgs, 6) promoters of the "Oneness" Pentecostal theory, and 7) God knows how many others.
For those who don't know, Arianism, named after Arius (ca. AD 250–336), and the eradication of which was the reason for the Nicene Creed, taught Jesus a divinely created Son of God, Savior of Mankind, subordinate to the Father. Jesus was "divine" but not fully God. More like a demi-God, the first born of all creation, second in charge, below the Father, but above every Angel.
Notable Arians who influenced the American Founding include Isaac Newtown, Samuel Clarke, Richard Price, Jonathan Mayhew and probably Johns Milton and Locke and many others. Arians likewise could answer the question "do you believe Jesus the divine Son of God" affirmatively, without having to assent to Trinitarian logic of 1+1+1 = 1, not 3, with which "rational" minded men might have a hard time.
John Jay, as I noted in my last post, at the very least flirted with Arianism/Trinity doubt.
Who knows what other great "Christian minds" struggle with Trinity issues?
Does that make them not "Christian"? Personally, I can't answer. Historically, though, non-Trinitarianism is labeled "heresy."
As noted above, Trinitarianism distinguishes itself from the more amorphous categorization of Jesus as the divine, risen Son of God. Trinitarians believe in that plus something else. It's that something else that distinguishes them.
That is if one asks the question: Do you believe Jesus Christ the divine, risen Son of God, 1) Trinitarians, 2) Arians, 3) Mormons, 4) Jehovah's Witnesses, 5) Swedenborgs, 6) promoters of the "Oneness" Pentecostal theory, and 7) God knows how many others can honestly answer affirmatively.
Yet, only Trinitarians can answer the question "do you believe in a Triune God, that Jesus is Second Person in the Trinity" affirmatively.
And that's to say nothing of the other "Christians" that John Adams named -- "Universalists,...Priestlyans, Socinians,...Deists and Atheists, and Protestants ‘qui ne croyent rien [Protestants who believe nothing]" -- who were united along with the various sects of Arians and Trinitarians in a lowest common denominator of "general Christianity" that founded American politics.