Interested in the politics of the FBI? Check out:
Enemies, by Tim Weiner. A valuable pop history of the FBI’s secret intelligence activities. Any assumption you might have that the FBI has historically been an apolitical group of technocratic law enforcers will be immediately dispelled by this book.
There’s Something Happening Here, by David Cunningham. A scholarly study of the FBI’s perceptions of and responses to different radical and armed actors during the 1960s, based on extensive archival research. This book is part of the basis for my claims below about the views held by the American security apparatus of right-wing militias in the US – they need to be kept an eye on and sometimes need to be cracked down on, but are not existentially threatening or worth full-scale repression. The hard Left, by contrast, was totally baffling and perceived as deeply alien, even when not (or very lightly) armed.