World War II was a turning point in the history of religious liberty.  It was during this period that politicians started talking less about the importance of religion and more about the importance of religious freedom. The key: it provided a stark contrast with the Nazis and later the Communists.  Roosevelt listed religious liberty as one of the Four Freedoms. Around this same time, interfaith groups of clergy – a rabbi, a minister and a priest – fanned out across the country. By the end of the war, trios had spoken to more than 9 million Americans at 778 bases. After an intramural football game at Fort Benning, Georgia, the marching band formed a giant Star of David and played “Ein Keloheinu”—and then re-formed into a giant cross and played “Onward, Christian Soldiers.  Though it’s hard to locate the exact date, I think it was this period that gave us the birth of the a-rabbi-a-priest-and-a-minister-walk-into-a-bar joke.

Source: Office of War Information