For a couple timely case studies, see Inside the Trump Bunker, With Days to Go (Bloomberg) and Trolls for Trump (The New Yorker); also see On Twitter, Trump bots are out-tweeting Clinton bots 7 to 1 (Recode)
"One of the apparent advantages of online news is persistent fact-checking. Now when someone says something false, journalists can show they’re lying. And if the fact-checking sites do their jobs well, they’re likely to show up in online searches and social networks, providing a ready reference for people who want to correct the record.How the Internet Is Loosening Our Grip on the Truth - The New York Times
But that hasn’t quite happened. Today dozens of news outlets routinely fact-check the candidates and much else online, but the endeavor has proved largely ineffective against a tide of fakery.
That’s because the lies have also become institutionalized. There are now entire sites whose only mission is to publish outrageous, completely fake news online (like real news, fake news has become a business). Partisan Facebook pages have gotten into the act; a recent BuzzFeed analysis of top political pages on Facebook showed that right-wing sites published false or misleading information 38 percent of the time, and lefty sites did so 20 percent of the time."