The
Communist Party and its allies played an important role in the United States
labor movement, particularly in the 1930s and 1940s, but never succeeded, with rare exceptions, either in bringing the labor movement around to its agenda of fighting for
socialism and full workers' control over industry, or in converting their influence in any particular union into membership gains for the Party. The CP has had only negligible influence in labor since its supporters' defeat in internal union political battles in the aftermath of World War II and the
CIO's expulsion of the unions in which they held the most influence in 1950. After the expulsion of the Communists, organized labor in the United States began a steady decline. Historians disagree why the union movement never formed a labor party and why American workers have never embraced socialist parties in any numbers in the last ninety years. Some have argued that a strain of
American exceptionalism made U.S. workers resistant to parties that emphasized
class struggle; others have attributed the left's failure to its own successes in building strong unions, but at the cost of downplaying its own political and social agendas for the sake of unity or short-term gains. Others take just the opposite position: that the left lost its power to lead the labor movement by its ideological zig-zags. The CP's history within the labor movement can support all of these theses.