Exactly.
On that subject, I cannot recommend enough an episode of a Lawfare-related podcast (ChinaTalk) called "Hoover, Communism, and the FBI" [1], which explore the life of J. Edgar Hoover, the zeigeist of the early twentieth century, and an revisiting the "red scare" in light of the since declassified information of Russian spying networks on US soil.
Related to this is the "Venona project" [2], where US agency could break the encryption of old soviet telegraph, and learn a great deal on soviet spy network.
[1] https://www.lawfareblog.com/chinatalk-hoover-communism-and-f...
[2] https://www.lawfareblog.com/lawfare-podcast-project-venona