I think it came up a little before 1947. Like I said in an earlier post, Thomas Jefferson himself wrote an explanation of constitutional intent:

"I contemplate with solemn reverence that act of the whole American people which declared that their legislature should "make no law respecting an establishment of religion, or prohibiting the free exercise thereof," thus building a wall of separation between Church and State."

I guess Jefferson was a true liberal and would have no place in present day America.