This is something I've been pressed on by some co-bloggers of mine. I'm answering now in part because I think the Glenn Beck rally in some profound way reflects why the American Founders driving the Trinity from politics mattered.
In my last post I wrote,
... What was the main area that connects all of the "key Founders" in their personal and political theology: The idea that there is a Providence and future state of rewards and punishments. The other doctrinal issues (especially whether Jesus was 2nd Person in the Trinity) where religions differ are superfluous and insignificant.
That's the lowest common denominator of "religion" that all good men believe in. That's why Calvinists, Swedenborgs, Jews and, today, Mormons (perhaps even Muslims; at least the good Muslims who peacefully demean themselves under America's civil law, which I would argue is the overwhelming majority of them) can feel communion with the God who "founded" America.
My American Creation coblogger the Rev. Brian Tubbs responded:
Jon, I don't agree with your assessment that doctrinal issues, including the deity of Jesus, are "superfluous and insignificant." I think some of those issues are crucial, and many of the Founders would've likewise considered them significant. It's unlikely, for example, that you'd get Noah Webster to refer to the deity of Christ as superfluous.
But I agree with you that monotheism combined with a future state of rewards and punishments was a common unifier, esp when you add TVD's clarification about God-given rights.
[Let me note as an aside that Webster may not have been an orthodox Christian during the Founding era when he was applauding the US Constitution as an "empire of reason" and looking forward to the progress of the French Revolution. But his statements in the early 19th Century do certainly reflect those of an orthodox Christian Americanist.]
When examining the words of the "theistic rationalists" or "Christian-unitarian-universalists" J. Adams, Jefferson, and Franklin, we see they wavered in their theology between bitterly rejecting the Trinity and orthodox doctrines as "corruptions" on the one hand (if that's the case then how could they feel communion with Trinitarians?) and terming those doctrines insignificant on the other (in that sense they COULD feel communion with Trinitarians).
I don't get any of the bitter rejection of the Trinity from Madison and Washington and I get less of it from Franklin than from TJ and JA. But I do sense the Trinity and other orthodox doctrines utterly insignificant to GW and JM. I judge this chiefly because, in their public AND private words, their God talk, JM and GW, while commonly speaking of "Providence" virtually ignored the Trinity and other orthodox doctrines. So if we were going to draw a lowest common denominator among all five of those "key Founders" perhaps we could say rejection of orthodox Trinitarian doctrine is a tenet. But to include JM and GW might be a stretch, even though I personally believe both of them privately rejected orthodox Trinitarian doctrine.
It would be more cautious then to form an LCD of those five around Providence, where the Trinity, Incarnation, Atonement, eternal damnation, etc. were superfluous and insignificant. And this is where their PERSONAL RELIGIOUS BELIEFS connect with their PUBLIC POLITICAL THEOLOGY.
Now, many of the 2nd tier orthodox Trinitarian Founders like Roger Sherman, Sam Adams, John Witherspoon likewise signed onto this non-sectarian Providentialist PUBLIC political theology while personally holding orthodox Trinitarian convictions as necessary for salvation an whatnot.
But they weren't the "key Founders." They weren't leading the show. Had they been, they could have formulated an orthodox Trinitarian political theology. They could have specified, when speaking on behalf of America, that the God whom they invoked was the Triune God of the Bible, perhaps put a Covenant to Him in the US Constitution. Or even if they stuck with the "no religious test clause," still made clear in the US Constitution that the God to whom they would pay homage was the Triune God of the Bible.
But they didn't. Instead we get a more generic inclusive Providence one that could unite evangelicals, Mormons, Jews and Muslims in political theological communion. The Triune God of the Bible could not do that.
So I hope that better answers the question as the why the non-Trinitarian religious convictions of the Founders made a difference.