If you really want to find a compelling starting point for the state of our current public political discourse, you may find it in the repeal of the Fairness Doctrine in 1987. Rush Limbaugh's first radio broadcast airs in 1988 which introduced "anger-tainment" as a very profitable political news model. As time passes, this new business model affected every news organization in one way or another, to various degrees, willingly or not.
https://en.wikipedia.org/wiki/FCC_fairness_doctrine