"The Puzzle Palace" was written in 1982. It's by an insider, James Bamford, and about his discovering by happenstance that people at the NSA listening post he was stationed at were listening in on american conversations illegally.

He also discovered that the Carter administration's justice department had opened a criminal investigation on the NSA, and through FOIA managed to get a copy of the file. It was pretty damning stuff.

This was 1982. What changed because of this?

https://theintercept.com/2014/10/02/the-nsa-and-me/