Regardless of what the founding fathers have been quoted with saying, the tangible fact remains that the U.S. was not founded on biblical law, as evidenced in the First Amendment, which reads:

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof

John Adams, et al, can have said whatever they liked. The fact remains that on paper and according to the Constitution, the U.S. is not now nor ever has been founded on biblical law. For that matter George Bush Jr. has made similar remarks about his god. That doesn't change matters.

Now, if you wished to put forth the proposition that the U.S. should be based on biblical law that's one thing. But to say that it once was and no longer is is historically false. No quote from the mouths of our forefathers can override the law that is written on paper, set in stone.