The right answer is Communist spies in the United States and social welfare programs .
It is not today that the US faces Russian spies, many believe, that these spies can influence the American political system, corrupting it and making it communist.
On the other hand, social welfare programs have a sense of 'helping' entrepreneurs (owners of capital) and workers, softening the asymmetric and savage relationship between capital and labor. This is also seen as communist threat because it strengthens the working class, which was one of the principles espoused by Carl Marx.