The Constitution and the Separation of Church and State
Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
Christine O'Donnell has been widely mocked for expressing doubt as to the presence in the Constitution of separation of church and state. As you can see from the First Amendment, quoted in full above, she is correct and her critics are mistaken. Not only do the words not appear in the Constitution, the idea does not appear either. Establishment of religion was a well understood concept; it meant an official state church, supported by government money. England had had such an arrangement since at least the sixteenth century and still does. So, currently, do Denmark, Norway, and Iceland (all Lutheran), as well as lots of Muslim countries. When the First Amendment was passed, Connecticut and Massachusetts had established churches.
Teaching creationism in the public schools—not a burning issue in those pre-Darwin and pre-public school days—is not an establishment of religion. Nor is having the government contract with religious groups to do things it wants done. The modern concept of the separation of church and state, based on a phrase used by Jefferson, is a creation of the courts that goes well beyond the language of the First Amendment. For details, see this post by Jim Lindgren, who teaches law at Northwestern.
That so many observers took it for granted that O'Donnell was demonstrating her ignorance rather than theirs is testimony to the power of that particular civic myth.