The FBI's practice of tracking "suspected communists" literally comes from the Red Scare. The McCarthyist era, which you seem to be calling "The Red Scare", is known as "The Second Red Scare". The First Red Scare followed the October Revolution pretty much immediately, and is the condition under which the FBI started surveiling suspected communists in 1919.
When Qian was asked to testify against Sidney Weinbaum, it was during the Second Red Scare.
All of this is absolutely tied up with those moral panics.