When Sen. Bernie Sanders of Vermont conceded the 2016 Democratic presidential primary to former Secretary of State Hillary Clinton and encouraged his supporters to vote for her in the general election, many of them agreed that Clinton—shortcomings and all—would be much better for his liberal/progressive movement than GOP nominee Donald J. Trump. Sanders aggressively voiced his support for the centrist Clinton during his speech at the 2016 Democratic National Convention in Philadelphia, stressing that a Trump presidency would be terrible for the United States (an assertion that proved to be frighteningly accurate). The “Bernie or Bust” crowd, however, adamantly maintained its opposition to Clinton: some voted for Green Party nominee Jill Stein or Libertarian Party nominee Gary Johnson (a former Republican governor of New Mexico), some didn’t vote at all, some even voted for Trump. And the Washington Post, in an article published on Friday, is reporting that some of Sanders’ more anti-Clinton supporters may have been manipulated by the Kremlin three years ago.

Russian interference in the 2016 election and President Vladimir Putin’s preference for Trump over Clinton was probed extensively by Special Counsel Robert Mueller, whose Russia investigation concluded in March. But one thing that hasn’t been reported nearly as much is efforts by the Kremlin to manipulate and deceive Sanders’ supporters. And in the Washington Post, Michael Kranish reports that three years ago, there was a concerted effort by Russians to convince Sanders supporters that they would be better off under Trump.

Kranish reports that in 2016, a Twitter account called Red Louisiana News told Sanders supporters, “Conscious Bernie Sanders supporters already moving towards the best candidate Trump! #Feel the Bern #Vote Trump 2016.” And analysis by Clemson University, according to Kranish, found that Red Louisiana News was among thousands of pro-Trump online accounts that were actually based in Russia—not the United States—and stressed to Sanders supporters that they had more in common with Trump than with Clinton. Kranish also reports that Mueller, during his Russia investigation, alleged that a St. Petersburg, Russia-based group called the Internet Research Agency instructed its employees to write social media posts that were anti-Clinton but favorable to Sanders and Trump.

In a 2018 interview, Kranish notes, Sanders told Vermont Public Radio that in 2016, one of his campaign workers suspected that Russians were behind those posts and warned the Clinton campaign, “I think these guys are Russians.” Kranish adds, however, that the campaign worker didn’t share those concerns with Sanders himself.

Sanders also told Vermont Public Radio that in 2016, Russian government operatives “were playing a really disgusting role” in the election and set out to “sow division in this country.” The senator commented, “What they were saying is—in so many words—is Bernie Sanders is not going to win. So if you are a Bernie Sanders supporter, let me tell you: Hillary Clinton is a criminal, a murderer, a terrible person…. crazy, all of these disgusting things.”

Clemson University’s research, Kranish adds, found that “some 9000” tweets coming from Russia used the name “Bernie” and were retweeted 61,804 times and “liked” 59,281 times.

One of the Russian social media accounts mentioned in Kranish’s article called itself #BlackMenForBernie, had 72,121 followers and tried to convince African-American Sanders supporters that they shouldn’t support Clinton. One of its tweets read, “#BlackMenForBernie Leader Switches to Trump! I will Never Vote for Hillary, Welcome aboard the Trump Train.”

Kranish concludes his report by quoting Clinton spokesman Nick Merrill, who warns that if people in the Russia government were able to manipulate the 2016 presidential election, they inevitably “will strike again.” And therefore, Merrill asserts, “Democratic candidates” must “work together and support each other to defend against these threats.”