From The Life and Times of Bruce Gerencser:
In the 1950s, thanks to men such as there’s-a-red-under-every-bed Catholic Congressman Joseph McCarthy, American Christianity’s God found a home in the Pledge of Allegiance and on the back of our paper money. Under God was added to the Pledge (1954) and In God we Trust was added to American paper currency (1957). In 1957, President Dwight Eisenhower signed a bill into law that stated the national motto was In God we Trust. These blatantly unconstitutional acts are still with us today. In 1954, then-Senator Lyndon B. Johnson proposed an amendment to U.S. tax code that would forbid churches and other non-profit, tax exempt institutions (501(c)(3)) from endorsing and campaigning for political candidates. This amendment is currently part of the tax code.