To the Right Wing the Popular Front was a nest of Soviet secret agents and party operatives. As Michael Denning writes in The Cultural Front, tales of espionage were very popular then as now and served as a way for people to wrap their minds around the clash of competing ideologies. To many anti-Communist Americans, supporters of Stalin and the Soviet Union were likely to be secret agents and the Popular Front existed only to aid and abet subversive activities and spread propaganda. This viewpoint was fed by the testimony and writings of many former Communist Party apostates.
The Left had in its own conspiracy theory. To them the postwar US government was controlled by a cabal of Nazi agents, British operatives, anti-Semites, Klansmen and Wall Street tycoons who were plotting to start World War Three and return Europe to Fascist control.
Denning concedes that the Soviet spy apparatus did use the Popular Front network to recruit agents, gather information and spread propaganda. However he disagrees that the Popular Front was created for this purpose. He makes a comparison to Yale University where he teaches. Many faculty members at Yale have worked with US intelligence agencies. Many Yale alumni have held high positions in these agencies. This does not, however, mean, he points out, that Yale exists to recruit and train CIA agents. However, a more apt comparison would be to the relationship in early years between the Puritan religion and Yale University. Yale was expected to uphold and propagate the tenets of the faith although it also served broader purposes. The same was true of the Popular Front.
Denning also dismisses the assertions of those who were actively involved in the Popular Front that they were naive dupes who had no idea that they were supporting the policies of the Communist Party or the Soviet Union. He believes that even though most active participants in the Popular Front were not Communist Party members they shared a world view with the Party. However Denning's theory would not necessarily include every individual who signed a petition, attended an event, or joined a union.