Known, open CPUSA members were and are the very least of the problem. It is the UNKNOWN communists who were, and are the problem.
Check Venona. agents of influence tended NOT to be CPUSA members and even were usually instructed to avoid commie front organizations. The abopve is not to say that CPUSA members and commie front stooges were not harmful, merely that the bigger fish swim deeper.
You are absolutely correct, only these other bums are much harder to trace. Here is what one Obama supporter wrote in People's Weekly World, the official newspaper of Communist Party USA.
"Obama’s victory was more than a progressive move; it was a dialectical leap ushering in a qualitatively new era of struggle. Marx once compared revolutionary struggle with the work of the mole, who sometimes burrows so far beneath the ground that he leaves no trace of his movement on the surface. This is the old revolutionary 'mole,' not only showing his traces on the surface but also breaking through."
-Frank Chapman, in PWW, Jan. 12, 2008
http://www.pww.org/article/articleview/12302/1/405