Oh good heavens, that's awfully late! Jefferson was a staunch advocate for the principle, but the Bill of Rights was passed in 1791 and the First Amendment is very clear on the point.

Maybe not quite as crystal clear as Jefferson's wall, but "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof" is pretty darn clear. You can't support it and you can't stop it with government. That's the separation of Church and State.