Bernie Sanders inspired a political movement with his insurgent 2016 run for the Democratic presidential nomination. Yet he's been reluctant to acknowledge that his campaign likely got some help from a Russian covert propaganda campaign.

What the Mueller indictment tells us

The allegations are laid out in a recent charges by Special Counsel Robert Mueller.

The 37-page indictment handed down last month includes dozens of allegations that Russians stole Americans' identities and created fake Facebook and Twitter accounts that worked as internet trolls designed to sow discord in the campaign.

These fake groups even staged political rallies, including one that featured an actress playing Hillary Clinton in a cage.

And part of the effort was designed to assist Sanders, the special counsel said.

The defendants "engaged in operations primarily intended to communicate derogatory information about Hillary Clinton, to denigrate other candidates such as Ted Cruz and Marco Rubio, and to support Bernie Sanders and then-candidate Donald Trump."

The indictment quotes a specific order given to the covert campaign to "use any opportunity to criticize Hillary and the rest (except Sanders and Trump — we support them)."

Sanders, a potential leading contender in the 2020 presidential contest, has tried to minimize the Russian meddling on his behalf.

But there's plenty of evidence of the Russian effort to help Sanders, including documents compiled the Democratic staff on the House Intelligence Committee and an NBC News database of roughly 200,000 tweets traced to the Russian trolls.

EXPLORE: NBC News' Full Database Of 200,000 Russian Troll Tweets Deleted By Twitter [Feb. 14, 2018]

For example, a Russian Twitter account called "Missouri News" (@MissouriNewsUS) sent out pictures of Sanders and President Franklin Roosevelt with the line "Bernie Sanders is basically a New Deal Democrat, #feeltheBern."

Ben Nimmo, an expert on disinformation campaigns who works for the Atlantic Council, a Washington, D.C-based think tank, said he and other experts saw signs of Russian meddling in early 2016.

The two-front cyber war included hacks and leaks of Democratic Party emails, including those by John Podesta, Clinton's campaign chairman.

The second front was the online propaganda war — run mainly by a company in St. Petersburg called the Internet Research Agency — that set up dozens of fake accounts supporting Sanders and Trump and opposing Clinton.

"There's a lot of focus now on the troll campaign, a lot of focus on the Internet Research Agency, but actually my sense if you had taken the hacking and the leaking — particularly the Podesta leaks, that was the heaviest punch landed on the Clinton campaign," Nimmo says.

Nimmo singled out the Podesta leaks because in the final weeks of the campaign, Clinton and her campaign were forced to respond to daily negative news stories.

"One of the things the Clinton campaign was having to do was firefight the Wikileaks/Podesta leaks, every day for a month before the election. That's a colossal burden for any press operation," he says.

The two fronts combined had an impact, Nimmo says. But — because you can't read the minds of individual voters — it's impossible gauge exactly how much it moved the electorate.

Yet Nimmo says there's no question it had an effect.

"When you put together the trolling, the propaganda, the leaking, all together, all interlocking, all amplifying each other, and then feeding into the febrile atmosphere of an American election, that's when you really get the damage being done," he says.

Other Facebook sites and Twitter accounts imitated Black Lives Matter or Muslim advocacy groups. And some were aimed at getting people not to vote.

"You had apparent Black Lives Matter accounts run from Russia telling African Americans it's better not to vote at all than vote for Hillary Clinton," Nimmo says. "So a classic vote suppression operation."

What Sanders has to say

Sanders, for his part, first downplayed the Mueller indictment's assertion that the Russian trolls were ordered to help his campaign.

In an interview with host Jane Lindholm on Vermont Edition, Sanders said the Russian social media campaign was aimed at hurting Clinton — not helping him.

Listen: Sanders' interview with Vermont Edition

You can find the exchange at ~11:31 in the audio above.

"Supporting my campaign, no, they were attacking Hillary Clinton's campaign and using my supporters against Hillary Clinton," he says.

Challenged by Lindholm, Sanders then says that one of his own campaign workers alerted the Clinton camp in September 2016.

"Turns out that what he was noticing — now we're into September, late into the campaign — he was noticing that hundreds of folks he had never heard of, names were suddenly coming into to Bernie Sanders Facebook, and they were attacking Hillary Clinton in all kinds of ways," Sanders says. "He checked it out and he went to the Clinton campaign and said 'you know what, I think these guys are Russians.'"

Pressed by Lindholm exactly what the campaign knew, and when, Sanders replied: "We knew what we knew when we knew it, and that's about all that I can say."

Reporting by Politico has challenged Sanders version of events.

Edward-Isaac Dovere, chief Washington correspondent for Politico and host of its Off Message podcast, unraveled the story after Sanders' appearance on Vermont Edition.

When I asked why Bernie Sanders was telling a story that he didn't verify and turned out not to be true, Sanders spokesperson told me he's "not a great fan of reporters who try to provoke controversy where none exists" https://t.co/YezgA32UjX — Edward-Isaac Dovere (@IsaacDovere) February 24, 2018

"This is a very specific assertion that Sen. Sanders made that his campaign sought to help Clinton's campaign by providing information about Russian troll operation. None of that is true," Dovere says. "It was a volunteer who talked to someone who supported Clinton's campaign, and there was no direct effort from the Sanders campaign on behalf of the Clinton campaign or anyone else."

Dovere covered the 2016 election and recalls attending Sanders rallies that drew thousands of people.

Obviously that support was genuine and not manufactured in St. Petersburg.

Still, Sanders seems reluctant to admit that not all of it was real.

"I think that they did not want to acknowledge that there were issues here raised by the Mueller indictment," Dovere says. "It's an uncomfortable situation to be in to be told that there were foreign entities supporting your campaign, even if you did not know that it was happening or didn't support that it was happening."

The Data explained:

The number of Russian troll accounts may seem insignificant at first, but these 105 tweets were retweeted 1,647 times, and this is just one pro-Bernie hashtag. Similarly, when filtering out trolls with >1,000 followers from NBC News' overall data (not just #FeelTheBern,) we can see that they sent over 140,000 tweets, and of those they were retweeted 420,000 times.

Again, this is an incomplete dataset, so the true extent is hard to pin down, but the impact of a few accounts can quickly be compounded by the power of their reach.

Why does this matter?

Two reasons, said Dovere.

Sanders is now a front-runner for the Democratic nomination in 2020.

And the Russian effort was coordinated, well-funded and aimed at the heart of American democracy.

Dovere said the Vermont senator's response is important, and the Russian meddling is still a story the American public needs to know.

He recently interviewed former CIA director Michael Hayden for Off Message.

"And what he said to me was this was an effort to mess with our heads and the Russians decided the best way to create chaos and mess with our heads was to support Donald Trump. Before they landed there, they were supporting Bernie Sanders," Dovere says.

RELATED - "Bernie Sanders Promoted False Story On Reporting Russian Trolls" [Politico, Feb. 24, 2018]

Ben Nimmo of the Atlantic Council agreed that the Russian influence has to be called out.

He found specific cases where fake news was cycled through Russian troll accounts, picked up by other web sites, then quickly parroted by Donald Trump.

"One of the earlier batch of Podesta leaks had come out and then an anonymous internet troll cut out one single paragraph from one single email and used it to claim that Clinton advisor Sidney Blumenthal was blaming her for the death of American diplomats in Benghazi," Nimmo says.

"That quote was then posted to reddit to a known haven of trolls, but it didn't go viral ... until almost simultaneously two accounts tweeted about it. One of those was an account called "MicroChip," which claims to be American; the other was an account called @Ten_GOP, which we now know was run by the troll factory in St. Petersburg. Those two accounts tweeted the same quote and that's what sent it viral. Within a few hours then-candidate Donald Trump read out exactly the same quote."

Nimmo pointed out the cause and effect of the hacking and the trolling working together to influence American voters.

"So there you have an occasion where Russian hackers have stolen an email. An anonymous troll posts it online. It's amplified by other trolls including a known Russian account, it's posted to reddit, and from one of those sources within a few hours that quote ends up in the in the mouth of a presidential candidate," he says.

Sanders campaign strategist Jeff Weaver did not respond to requests for an interview.

In a statement released after the Vermont Edition interview, the Sanders campaign condemned the Russian conduct and acknowledged the effort helped campaigns in 2016 "including my own."

Update 03/02/2018 10:18 a.m. This story has been updated to provide more clarity around the NBC News Russian Troll data.