First of all HUAC was used as a pejorative -- The House Committee on un-American Activities I believe is the correct name.
McCarthy was a Congressman in the late 1940s and participated in controversial hearings which his enemies used to brand him a Nazi. Then when he took on communism that was the end of him.
W.W.II was the last war that the "progressives," "leftists" whatever sided with the U.S. The U.S. helped defend their Uncle Joe.
Clarification: he was a Senator.