Russia’s interference in the 2016 U.S. election has generally been seen as two separate, unrelated tracks: hacking Democratic emails and sending provocative tweets. But a new study suggests the tactics were likely intertwined.

On the eve of the release of hacked Clinton campaign emails, Russian-linked trolls retweeted messages from thousands of accounts on both extremes of the American ideological spectrum.

Those retweets increased the odds selected Twitter users would be online and able to express outrage when the next day on Oct. 7, details such as the revelation that Clinton may have had early access to a primary debate question were released.

Those retweets also brought those lesser-known users a wider audience, encouraging them to tweet more, and ultimately helping polarize American public debate.

In the study, Clemson University professors Darren L. Linvill and Patrick L. Warren say messages were retweeted from some 4,000 accounts on Oct. 6, 2016, the day before Wikileaks’ release of hacked emails belonging to Hillary Clinton’s campaign chair, John Podesta.

Through the retweets, Russian trolls amplified messages on the fringes of American politics. Twitter users, especially on the far left, responded negatively to revelations about Clinton, fulfilling Russia’s attempt to boost Donald Trump’s candidacy and add to the divisiveness in American politics.

Ultimately, those retweeted users gained a total of 500,000 new followers over the next four days, the study found. The increase in followers apparently prompted the Twitter users to tweet more. The report found that overall, they had sent 600,000 more tweets over those four days than they would have otherwise. The researchers based this figure on a comparison with similar Twitter accounts that had not had a retweet from a Russian troll during that period.

The research was supported by a Charles Koch Foundation grant. The authors say the foundation and its conservative leader did not influence the findings, which are in line with other, bipartisan research on Russian meddling in elections.

In a statement, Twitter said, it is “committed to fostering free and open democratic debate around the globe. We’ve made significant progress since the 2016 U.S. election to address, mitigate, and prevent future attempts to undermine the integrity of online conversation regarding elections and the democratic process.”

While the existence of a spike in Twitter activity on Oct. 6, 2016, has been known and the authors prior work was cited in Tuesday’s release of a Senate Intelligence Committee report on Russia’s use of social media during the election, exactly what those trolls were up to has not been previously detailed.

U.S. authorities have often pointed to Russia’s use of fake and ideologically extreme Twitter accounts — or trolls — to spread disinformation. The Senate report detailed a complex and highly effective campaign via the Russian government-affiliated troll farm, known as the Internet Research Agency, or IRA.

But the retweeting strategy has received less notice and may have a more lasting impact.

The retweeting marked a deliberate change in tactics. It remained in full force during the last month of the election, with the IRA, retweeting from an estimated 25,000 accounts and, in turn, making those users more active: They sent some 4 million tweets they otherwise would not have sent, according to the statistical analysis — and gained 3 million additional followers.

The 4 million retweets in one month greatly surpasses the total 2.8 million unique tweets sent by Russian trolls during the three-year campaign ending in 2017.

While Twitter ultimately suspended the fake accounts, roughly 90% of the more ideologically extreme Twitter accounts that the Russians pushed to greater prominence remain active and contribute to the more polarized public debate today.

“Twitter can go and delete all the trolls, and what the trolls said, but this amplification effect is still there,” Warren said. “It’s like an infection. You can remove whoever was patient one in the infection, that’s fine, but if the infection’s already started, it’s too late.”

The report marks the culmination of two years of study by the professors, whose prior work of Russian troll activity has been picked up by national security agencies and the Senate Intelligence Committee

The professors zeroed in on Oct. 6 because that’s the day both left and right ideologically aligned trolls went from merely building their identities on the social media platform to suddenly using those personas to build up selected existing users, especially retweeting users on the far left.

Warren and Linvill call this a possible “new type of agenda setting” where a big part of the information operation conducted by the Russian government is changing the voices that are prominent in a political conversation and, indirectly, change the tenor of the conversation.

Sarah Mendelson, a professor of public policy who heads Carnegie Mellon University’s Heinz College in Washington, said the report fills in details on the Kremlin’s strategy.

“There’s even more cohesion to the IRA plan than we thought,” said Mendelson, who has extensively studied Russian disinformation campaigns.

Mendelson noted that Oct. 7, is not only Vladimir Putin’s birthday, but the day U.S. officials publicly stated that the Russian government was behind the election hacking that targeted Democrats, and the day the Washington Post published the Access Hollywood story and audio that included Trump making lewd comments about women.

While some have thought the WikiLeaks release of Podesta’s hacked emails was timed to detract from the Access Hollywood story, the professors say the clear Russian strategy of retweets started the day prior indicates that it’s more likely the timing of events was a happy coincidence.

The report found that the “left trolls” tended to target ideologically similar accounts that were also often part of the Black Lives Matter movement and used “black” in their description. “Right trolls” tended to retweet and reply to accounts that had account descriptors like “MAGA” and “Conservative.

(AP)