Alex Tabarrok reports at Marginal Revolution on the 1796 treaty with Tripoli, and in particular the famous Article 11 saying that "the government of the United States of America is not in any sense founded on the Christian Religion...". He adds that this was "read aloud in the Senate and approved unanimously."

I would personally like this to be true, but at the moment I'm inclined to believe the story as told by the Yale The Avalon Project : The Barbary Treaties 1786-1816 which says that what was approved by the Senate was the "Barlow translation", and that

As even a casual examination of the annotated translation of 1930 shows, the Barlow translation is at best a poor attempt at a paraphrase or summary of the sense of the Arabic; and even as such its defects throughout are obvious and glaring. Most extraordinary (and wholly unexplained) is the fact that Article 11 of the Barlow translation, with its famous phrase, "the government of the United States of America is not in any sense founded on the Christian Religion," does not exist at all. There is no Article 11. The Arabic text which is between Articles 10 and 12 is in form a letter, crude and flamboyant and withal quite unimportant, from the Dey of Algiers to the Pasha of Tripoli. How that script came to be written and to be regarded, as in the Barlow translation, as Article 11 of the treaty as there written, is a mystery and seemingly must remain so. Nothing in the diplomatic correspondence of the time throws any light whatever on the point...

So at the moment, I'm not buying it.

[UPDATE: A.T. replies that the "key point" is precisely that the Barlow translation with its "not in any sense founded on" phrase was approved, published in newspapers, &c, so that the mere fact that it wasn't part of the treaty as seen by Tripoli has nothing to do with his post. And he's right, and I'm wrong again. (And I have also committed and fixed several Javascript errors this morning. Mostly by moving tested code into more appropriate places with insufficient testing.) So it goes.]

[WHY? I want to think more about why I make particular mistakes. In this case, the correct reading is not a surprise, so I don't believe I was biased against it: I model the Founders mainly as a mixed bag of Christians (Adams) and quasi-Christians (Jefferson, with his miracle-free Bible) and Deists (Franklin) with occasional Jews and very few and quiet atheists. Anything monotheistic would be fine with them, and they would certainly accept Article 11. So why did I fail to read carefully? In this case, I was simply rejecting the whole thing as bogus: I remembered (from a year or three ago) that the Barlow translation was not the "real" treaty, and on recovering the Avalon Project passage that supported my memory, I simply stopped there. If I'd treated it as a program-design issue, tracing the values on each side of the translation, I would not have made the mistake--but I would have had to do some extra thinking. Well, it's a fair trade-off, as long as I'm not too easily embarrassed. Incidentally, I hereby conjecture that the Barlow translation is a correct translation of what the translator was given, and that an unimportant letter was then inserted in the Arabic as part of a plot to prevent possible friendship between moderate Muslims and the U.S. Hey, as long as I'm making mistakes, I might as well try to make interesting ones...