No. No it wasn’t.
Pharyngula links to the webpage of the Family Research Council, which currently holds a poll titled, “Do you believe that America, as a nation, was founded upon Christian principles?” Due to the Pharynguloid influence, “No” is currently leading at 91%, but that’s not the point. The point is that this question should not be asked in the first place.
The US is emphatically not founded on Christian principles. This is explicitly stated in the Constitution, both in the First Amendment (“Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof;”) and in Article VI, section 3 (“…no religious test shall ever be required as a qualification to any office or public trust under the United States.”) In addition, the Treaty of Tripoli, itself a legally binding document, bears these words: “As the Government of the United States of America is not, in any sense, founded on the Christian religion…”
The United States is a secular nation, not a Christian nation. Any claim to the contrary is founded in ignorance of the Constitution, or in delusion. Check mate, I’m afraid, for the Dominionists.