America's Protestant fundamentalists, Pentecostals, and Roman Catholics have often been divided sharply by theological and secular issues. In the 1930s and 1940s, however, they were united in their opposition to "atheistic Communism." Monsignor Bishop Fulton Sheen and Father Charles Coughlin took to the radio in the 1930s to decry what they saw as the Soviet Union's policies of repression at home and subversion abroad. Pittsburgh "labor priest" Charles Owen Rice helped build the Association of Catholic Trade Unionists (ACTU) in 1937 to combat Communist influence within the Congress of Industrial Organizations (CIO).

Given the great number of Catholic CIO members, as well as their prominent leadership roles in the union movement, labor heeded the advice of Rice, Sheen, and Francis Cardinal Spellman to reject "red fascism." Representing 16 percent of the U.S. population in 1940, but accounting for one-quarter of the Democratic Party's national...