"God bless you, and God bless the United States of America." - Ronald Regan , the patron saint of today's Republican party

When it comes to running for the highest office in the United States, being on good terms with Jesus seems to be just as important as having a good grasp of foreign policy, or a sound plan for the economy.

"In God We Trust" first appeared in 1957, following a 1956 act of Congress that declared the phrase the national motto of the United States. ( Alex Wong/Getty Images)

That may seem like a gospel truth in U.S. politics today, but according to the Princeton University history professor Kevin Kruse, it hasn't always been so.

In a new book, he traces the origins of that religious litmus test back to a forgotten moment during the Great Depression when big business suddenly got religion.

The book is called "One Nation Under God: How Corporate America Invented Christian America."

Kevin Kruse joined Anna Maria from Princeton, New Jersey.

President George Bush Stands With Billy Graham, January 19, 1991. Graham declared at the time that present war in the Gulf is a "fight for peace" which will result in a "New World Order" as suggested By President Bush. (Getty Images)

It was in the wake of the 9/11 attacks that then-president George W Bush announced a "crusade" against terror. And he did come into a fair bit of criticism for choosing such a religiously- and historically-loaded term as "crusade."

But the U.S. does have a long history of infusing its wars with religious meaning.

Andrew Preston has chronicled that relationship in his book "Sword of the Spirit, Shield of Faith," which won the 2013 Charles Taylor award for the Best Canadian work of literary non-fiction. He is a professor of American History at Cambridge University in England.



This segment was produced by The Current's Howard Goldenthal.