The FBI just released a voluminous file on progressive historian Howard Zinn.
The file alleges that Zinn was a member of the Communist Party in the late 1940s and early 1950s, though he steadfastly denied it when the FBI twice interviewed him.
Reading the file takes you back to the creepiest days of McCarthyism, as neighbors and ostensible friends ratted Zinn out to the FBI, and as agents would call up his landlords and employers seeking information. Even a postal carrier was used as an informant. The file shows that the FBI had informants throughout the Communist Party.