What Right Wing News did was part of a shift in the flow of online disinformation, falsehoods meant to mislead and inflame. In 2016, before the presidential election, state-backed Russian operatives exploited Facebook and Twitter to sway voters in the United States with divisive messages. Now, weeks before the midterm elections on Nov. 6, such influence campaigns are increasingly a domestic phenomenon fomented by Americans on the left and the right.

“There are now well-developed networks of Americans targeting other Americans with purposefully designed manipulations,” said Molly McKew, an information warfare researcher at the New Media Frontier, a firm that studies social media.

Politics has always involved shadings of the truth via whisper campaigns, direct-mail operations and negative ads bordering on untrue. What is different this time is how domestic sites are emulating the Russian strategy of 2016 by aggressively creating networks of Facebook pages and accounts — many of them fake — that make it appear as if the ideas they are promoting enjoy widespread popularity, researchers said. The activity is also happening on Twitter, they said.