I doubt many of the Founding Fathers would pass muster with most Christians nowadays. Probably not with those who practice a political sort of Christianity. (But one must admit they seem to have no doubt as to the state Donald Trump’s soul.)
The Founding Fathers were a bunch of eccentrics. They agreed on little, including religion I suppose.
But more to the point, does it matter? While I admit I am no expert on their beliefs, I assume they did not expect people two centuries later using ouija boards to determine how we ought to live. They are dead. We are alive. This is whatever sort of country we want it to be.