Amplified by bot swarms, Russian-linked Twitter accounts tried to foment discord before and after the election. Hundreds of accounts promoted false stories about Hillary Clinton and spread articles based on leaked emails from Democratic operatives that had been obtained by Russian hackers.

Facebook, Google and Twitter have, to varying degrees, announced new measures to eliminate bot accounts, and have hired more moderators to help them weed out disinformation on their platforms.

But since the election, the Russian-linked bots have rallied around other divisive issues, often ones that President Trump has tweeted about. They promoted Twitter hashtags like #boycottnfl, #standforouranthem and #takeaknee after some National Football League players started kneeling during the national anthem to protest racial injustice.

The automated Twitter accounts helped popularize the #releasethememo hashtag, which referred to a secret House Republican memorandum that suggested the F.B.I. and the Justice Department abused their authority to obtain a warrant to spy on a former Trump campaign adviser. The debate over the memo widened a schism between the White House and its own law enforcement agencies.

The bots are “going to find any contentious issue, and instead of making it an opportunity for compromise and negotiation, they turn it into an unsolvable issue bubbling with frustration,” said Karen North, a social media professor at the University of Southern California’s Annenberg School for Communication and Journalism. “It just heightens that frustration and anger.”

Intelligence officials in the United States have warned that malicious actors will try to spread disinformation ahead of the 2018 midterm elections. In testimony to Congress last year and in private meetings with lawmakers, social media companies promised that they will do better in 2018 than they did in 2016.