I see Jonathan as drawing a boundary too constrictive and impermeable around the Founding ideas. I cannot dispute that Jefferson and other deists (or whatever they all were--that's another ongoing debate in this space) viewed the Declaration of Independence—to use one important, concrete example—through the lens of their particular worldview. But does that mean that the text itself is not open, to some extent, to other interpretations through the lenses of other worldviews? To return to an earlier example, the Catholic signer of the Declaration, Charles Carroll, was not a theologian, but I'm not aware that anyone has questioned in general his Catholic orthodoxy. How could he sign the Declaration if it were simply, case open and shut, an expression of principles rooted in a worldview hostile to or at least inconsistent with a Catholic one? Did he misunderstand it? Was he dishonest? My own view is that he was neither and that he, like me some years later, can in good conscience fully subscribe to the principles articulated by the Declaration, even if he (like me) would want to qualify and clarify its meaning in a way that rendered it consistent with the Catholic tradition. That is not to say that the parameters of meaning are utterly amorphous: there are limits to how the words "inalienable rights" can be legitimately interpreted. Jonathan wants to set those limits relatively more narrowly; I want them to be more expansive.
This is not quite the point I was trying to make. I too agree that the Declaration can be read in an expansive way. But the language is so broad and expansive that, it seems to me, it is difficult for religious traditionalists to "claim" its ideas in an exclusive sense. I'm not saying that Kevin is trying to do this. If all he is arguing is that nothing in the Declaration's ideas should prevent traditional Catholics or Christians from embracing the document, he'll get no argument from me. But there are folks who do argue that the Declaration's content is exclusively biblical or traditionalist and that's the claim against which I argue.
The text of the Declaration of Independence contains broad guarantees -- "blank checks" if you will -- to such concepts as liberty, equality and the pursuit of happiness. An evangelical can look at the Declaration and see their biblical God as granting the right to live one's life as a good Christian. A Roman Catholic can look at the Declaration and see a document that complements their Aristotelean-Aquinas natural law tradition. Heck Mormons literally believe the Declaration to be sacred scripture. And social liberals can see blank checks to lifestyle liberty and the pursuit of happiness. This was Robert Bork's point in Chapter 3 of "Slouching to Gomorrah." And I agree with Bork and laud the Declaration for the reason Bork opposes it: The very text of the Declaration is quite amenable to my worldview that doesn't believe government has any role in "making men moral" (as Robbie George once put it) but rather believes simply government should protect men's rights and leave us alone. The Declaration talks about "rights," not duties and says men have a right to pursue "happiness," not a duty to pursue "virtue."
At this point, "Christian America" apologist usually note the God of the Declaration clearly was the biblical God or that its ideas are all "biblical," as though they "own" the content. But as an historical and philosophical matter, this is false. Sure the Declaration is compatible with a traditional biblical worldview; but it's compatible with all sorts of worldviews. It was a document written with very broad rhetoric and in a theological sense indeed can be all things to all people, or at least many things to many people.