With more than 10 million followers on Twitter, Mr. Sanders has a larger audience on the platform than Ms. Warren,
Pete Buttigieg,
Joseph R. Biden Jr. and Senator
Amy Klobuchar combined. A sizable number could be automated bots or fictitious accounts. Federal prosecutors have
detailed coordinated efforts by Russian nationals to interfere in the 2016 election, with an emphasis on two candidates — Donald J. Trump and Mr. Sanders — whom the Russians hoped to bolster while denigrating their opponents.