Puzzle Palace, published 1982: https://www.amazon.com/Puzzle-Palace-National-Intelligence-O...
This guy made a career out of documenting the inner workings of the NSA and what they get up to. It wasn't common knowledge, but it's been known what they get up to, and proof thereof, for decades.
I think The Puzzle Palace (https://www.amazon.com/Puzzle-Palace-National-Intelligence-O...) made the same argument as far back as 1982
https://en.wikipedia.org/wiki/The_Puzzle_Palace
https://www.amazon.com/Puzzle-Palace-National-Intelligence-O...
After reading that book and getting a better sense of the scope of intelligence operations over a wider swath of history, these types of requests come from make a whole lot more sense (whether you agree or not, you get a sense of the place they're coming from). Not making an argument in regard to what's right or wrong, but it does provide a tangible dose of reality. Also, given this was written in the 80's and much has come to be known since then, I still think this book holds its own in terms of clarity because it discusses historical topics without the messiness of the internet, social media, etc. Bamford has several more recent books, but I have not read those.