Columbia subject headings:
Communism--United States--1917-
Communism--United States.
Internal security--United States.
Security clearances--United States.
Subversive activities--United States.
Harvard subject headings:
Communism--United States
Communism--United States--1917-
Internal security--United States
Subversive activities--United States
Princeton subject headings:
Communism--United States--1917-.
Internal security--United States.
Loyalty oaths--United States.
Subversive activities--United States.