I remember watching a documentary on this like 7 or 8 years ago too...Comment sections on popular site have been overrun by alt right agents who are well organized...
There is a big movement behind the scenes of paid trolls hitting up comment sections...A lot of folk when they read an article or watch a video look at the comments section hence why they have been targeted by trolls...The trolls job is to discredit the article/video with Trump "fake news"...
That's why sites like yahoo are seemingly flooded with Trump supporters...A lot times its the same troll with 5 accounts hammering a popular article in an attempt to discredit it...