During the 1950s, Caldwell was an outspoken critic of the U.S. House of Representatives Un-American Activities Committee (HUAC) and of Senator Joseph McCarthy and his pursuit of alleged Communists through the Senate Permanent Subcommittee on Investigations.
In 1955, Caldwell organized a petition drive, signed by 135 of his USC faculty colleagues as well as ministers who were members of the Southern California Baptist Ministers Union, protesting the selection of Texas Governor Robert Allan Shivers (1949-1957) as USC Commencement speaker at the graduation ceremonies.