I have to disagree with you, by the "early 80's" the shift to the left was virtually complete in print and broadcast media. I used to be a voracious reader of news magazines (Time, Newsweek, USN&WR) starting in college (free library access). By the mid 80's the only one with even a pretense of impartiality was USN&WR, and that one made the leftward shift at about 1985.
What lost the press and the culture in general to the leftists, was the Viet Nam War and its protest movement. It’s that ding dong simple. It became clear then that globalist financier oligarchy had turned America into an EMPIRE. Empires eventually get what they deserve. Unfortunately America takes the blame for what a hand full of feudalist Nazi sympathizer oligarchs (Go ahead, research Prescott Bush & Co.) manage to pull off as the “invisible hand” of government.
Watch this video: https://www.youtube.com/watch?v=7XtEfnyylFk