MSNBC Host Actually Reads the Constitution AND STILL QUESTIONS O'Donnell

First Amendment: 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.

Separation of Church and state DOES NOT APPEAR in the Constitution.
The phrase was quoted by the United States Supreme Court first in 1878, and then in a series of cases starting in 1947. The phrase itself does not appear in the U.S. Constitution, what is known as the Establishment Clause with the First Amendment of the Bill of Rights states that "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof."

Everson v. Board of Education(1947) was the first prominent use of the phrase.Both Justice Hugo Black's majority opinion and Justice Wiley Rutledge's dissenting opinion defined the First Amendment religious clause in terms of a "wall of separation between church and state".
Black's opinion said....
"The 'establishment of religion' clause of the First Amendment means at least this: Neither a state nor the Federal Government can set up a church. Neither can pass laws which aid one religion, aid all religions or prefer one religion over another. Neither can force nor influence a person to go to or to remain away from church against his will or force him to profess a belief or disbelief in any religion. No person can be punished for entertaining or professing religious beliefs or disbeliefs, for church attendance or non-attendance. No tax in any amount, large or small, can be levied to support any religious activities or institutions, whatever they may be called, or whatever form they may adopt to teach or practice religion. Neither a state nor the Federal Government can, openly or secretly, participate in the affairs of any religious organizations or groups and vice versa. In the words of Jefferson, the clause against establishment of religion by law was intended to erect 'a wall of separation between Church and State.'" 330 U.S. 1, 15-16.