I think one thing that Christians and non-Christians can agree on (albeit for vastly different reasons) is that the Bible isn't rational. The Constitution, on the other hand, is hyper rational and was created through trial-and-error and a series of negotiated compromises. To suggest otherwise, based on a few select quotes about the nature of morality, several of which don't even contain reference to any sort of divinity, is incorrect revisionist history. We could each also post disparaging things that were said by the Founders in regard to Christianity, but that would be fighting fire with fire, so I will not do that. The fact that we can debate what morality even is is sufficient evidence that it is derived solely from critically thinking people.
I'm admittedly not a man of faith, so I don't have a deep understanding of it, but it seems to me (again, as an outsider) that part of the point of faith is to shed one's connection to the world of logic and rationality and try to gain some other type of experience (spiritual peace or enlightenment, for example, I suppose). On a related note, when I said the Bible was irrational, it was not meant as a pejorative. I'm not naive enough to think that hyper rationality is in any way a desirable way to live. There are many things that can't in principle be rationalized. To return to the Constitution, I think this can actually be a problem in our legal system. A courtroom is a forum where rationality is given great weight, and it can lead to strange outcomes, where, say, one man goes to prison for light shoplifting, while another goes free on a technicality after committing murder. I won't pretend to know a better alternative, but I think it is clear that rationality isn't always good or desirable.