It's hard to really encapsulate what Moyers meant to American media, particularly progressive media, without understand how far gone the US media environment was in the 80's; an era where the NYT's dominance in the national discourse was much greater than it is now, and Americans were legit getting their "news" from fucking Time Magazine (never, trust Time Magazine, they're basically Cold War We're The Good Guys" the rag).
The less said about his role in the Johnson administration, the better.