WTF Happened in 1971? (2019)
This video has a nice summary of all the changes in the 1970s, and how many other prominent authors have documented that radical  shift.
https://www.youtube.com/watch?v=1gEz__sMVaYThe author believes the problems can be traced to the US congress switching from closed (anonymous) to open voting on January 3rd, 1971Somewhat related, this post shows how the US congress has grown incredibly divided over time
https://www.realclearscience.com/journal_club/2015/04/24/pol...