Fake Facebook news contributed to brainwashing a couple of people I know. My mother and a close work colleague. My mother was a very leftist fun-loving person, but she leans toward conspiratorial influences. Facebook was rife with wacko conspiracies and most of them were pro-Trump. She's kind of come around now, but it did have a huge impact on her and lot of her American friends.
My co-worker believes that everything she reads in her Facebook sidebar is real news. I checked her feed out and some of the stories were fake news purporting to be from reputable agencies like the CBC or Reuters.
There's no downplaying it. It was and is still scary as hell how easily people can be influenced.