There is great dispute over how to properly understand the natural law that America's Declaration of Independence invokes. One side argues such an idea is entirely compatible with classical and Christian concepts of natural right and the other argues the Declaration's natural rights teachings are novel Hobbsean/Lockean and hence modern ideas.
Ellis Sandoz, a traditional Roman Catholic scholar at LSU argues contra Leo Strauss, for the traditional classical/Christian side of the natural law contained in the Declaration. He has a new book out on the matter which I'm sure makes an invaluable contribution to the debate.
I can't resolve who is right in the debate though my sympathies lie with the Straussian side which views the natural rights teachings of the Declaration to be "modern" and subversive of attempts to use politics to preserve the traditional Christian order.
However, one thing is undeniable, and unfortunately, all too often misunderstood by the Protestant "Christian America" crowd, but not by the traditional Roman Catholics for whose side Sandoz eloquently argues, and that is "nature" defines as what is discoverable by reason as opposed to revealed in the Bible. As such, the natural law or "laws of nature and nature's God" defines as what man discovers through reason alone. Now this could lead to some very conservative results; the traditional natural law scholars ala Aquinas, and in whose tradition Robert George, John Finnis, Hadley Arkes, and Ed Feser presently operate use natural reasoning to oppose among other things abortion, homosexuality, and contraception. Or using "reason" and the premise that man has unalienable natural rights to life, liberty, pursuit of happiness, property, equality, and conscience could also lead to very un-conservative, non-traditional outcomes. For instance, Locke's self ownership principle, part of this natural rights theory, could logically result in pro-sodomy, pro-contraception, pro-drug use, and perhaps pro-abortion outcomes. Indeed, Justice Stevens in the dissent in Bowers v. Hardwick noted "the concept of privacy embodies the `moral fact that a person belongs to himself and not others nor to society as a whole.'"
But the bottom line is, "reason" not "revelation" is where arguments over public policy are supposed to take place, according to whichever of the two views of the natural law/natural rights one endorses or thinks is endorsed by America's Declaration of Independence.
The reason why America had to turn to reason or the natural law to ground its public order was because the politics of revelation were too sectarian and lead to sectarian disputes. In order to overcome such disputes, revelation had to be driven from politics. Indeed sometimes Founders such as John Adams termed this rationalistic natural religion that served as America's civic religion, "Christianity"; but reading the context of those quotations shows what Adams was invoking was not traditional biblical Christianity, but something else.
For instance, one famous quotation that the "Christian America" crowd often offers out of context is (Sandoz's paper reproduces it as well):
"The general Principles, on which the Fathers atchieved Independence, were the only Principles in which that beautiful assembly of young gentlemen could unite.... And what were these general Principles? I answer [John Adams wrote]-- the general principles of Christianity, in which all those sects were united: And the general Principles of English and American Liberty, in which all those young men united, and which had united all parties in America, in majorities sufficient to assert and maintain her Independence. Now I will avow, that I then believed, and now believe, that those general Principles of Christianity, are as eternal and immutable, as the Existence and Attributes of God; and those principles of Liberty, as unalterable as human nature and the terrestrial, mundane system "(Letter of Adams to Jefferson, June 28, 1813).
So one might ask, what are these "general principles" of Christianity about which Adams was speaking? The Trinity? Incarnation? Atonement? Original Sin? Infallibility of the Bible? No! Adams vehemently rejected these notions especially in the year 1813 when writing this letter to Jefferson (many of Adams' most heterodox statements were written in that year). Adams states these "general principles of Christianity" drew a lowest common denominator among the following types:
"Who composed that Army of fine young fellows that was then before my eyes [during the American Revolution]? There were among them, Roman Catholicks, English Episcopalians, Scotch and American Presbyterians, Methodists, Moravians, Anabaptists, German Lutherans, German Calvinists, Universalists, Arians, Priestleyans, Socinians, Independents, Congregationalists, Horse Protestants, House Protestants, Deists and theists; and [Protestants who believe nothing]. Very few however of several of these Species. Never the less all educated in the general Principles of Christianity: and the general Principles of English and American Liberty.
[* Note Sandoz's version reads "Deists and theists"; the version with which I am familiar reads "Deists and Atheists."]
Arians, Priestleyans, Socinians, it should be noted, are unitarians. Universalists denied eternal damnation. Invoking these four groups as "Christians" was a sentiment heterodox enough, but understandable given those groups best represent Adams' own personal theology. Yet, Adams goes further and notes "Deists and Atheists; and [Protestants who believe nothing]" are part of this lowest common denominator of believers in "general principles of Christianity." As Dr. Gregg Frazer, himself an evangelical of impeccable orthodoxy, noted:
Adams spoke of the “fine young fellows” who conducted the Revolution. He said that they included all of the various denominations of protestants as well as “Deists and Atheists, and Protestants who believe nothing.” That is the context in which he speaks...of “the general Principles of Christianity, in which all those Sects were United.” The “those Sects” includes deist, atheists, and those who believe nothing. This was clearly not the Christianity of the orthodox, who did not believe that deists, atheists, and those who believe nothing were united with true Christians on any principles of Christianity!
So even those quotations that seem on point that the Christian America crowd offers out of context, when understood in proper context, support the notion that America's higher law is part of a naturalistic theology ascertainable from reason, not the Bible.
Where this dispute may be relevant in today's politics: On matters of legislation, I don't think if a number of politicians support a policy because the Bible tells them, that would be unconstitutional. Politicians can use any personal reason for voting for or against legislation. However, if scripture or revealed religion is the only possible reason that can be ascertained for a piece of legislation, I think that should flunk the rational basis test of judicial scrutiny. This dispute is more relevant on how the judiciary might approach the concept of natural law or natural rights. Currently, one member of the Supreme Court, Clarence Thomas, supports incorporating the Declaration of Independence's natural law/natural rights teachings into constitutional jurisprudence. And the historical record, in my opinion, strongly supports such an approach. At least this is something Supreme Court Justices seriously discussed in the Founding era, see Calder v. Bull.
Constitutional interpretation needs to be grounded in some kind of theoretical approach. And the natural law/natural rights approach is entirely consistent even demanded by the original meaning of America's Founding documents. If such an approach gains more appeal in the judiciary, it's paramount that we properly understand that the higher law of the natural law is that which is ascertainable from reason, not revelation.