Thanks for the kind words.
I am not sure that even-handed historians really exist—everybody, even folks I respect, seem to have an agenda or multiple agendas.
Probably the best book on the FBI during that period imho:
https://www.amazon.com/Official-Confidential-Secret-Edgar-Hoover/dp/0399138005
Somewhere in my family archives is a letter from J. Edgar Hoover to my Dad. It was concerning the increasing dangers of communist infiltration.