Russia's coordinated effort to nudge Americans toward voting for Donald Trump in the 2016 presidential election caught social media companies flat-footed and remains a stain on the reputation of Facebook in particular.
Four years later, the FBI and other American security officials -- aware of interference but silent last time -- are warning that Russia and Iran are meddling.
But Russia's actions -- special counsel Robert Mueller's report detailed the Kremlin's bias for Trump and antipathy toward Hillary Clinton in 2016 -- and those of other countries are only part of the disinformation problem.
Americans are now playing the leading role, posting the bulk of false or misleading comments, memes, photographs and videos that are spread with the ease and speed of online distribution. And there are signs that it is out of control.
"What the Russians did in 2016 was show a toolkit, where you could use deceptive actors online working in coordination with each other as a political tool," Joshua Tucker, a professor of politics and expert on data science and social media at New York University, told AFP.
"There's been a fixation on foreign interference, but the people who really have an incentive to influence the outcome of an election are people who live in that country -- Americans."
Facebook's latest report about inauthentic behavior confirms the trend.
Sowing political discord
In the first week of October alone it took down 200 Facebook accounts, 55 Pages and 77 Instagram accounts that originated in the US.
Copying the Russian tactics of 2016, the operators used stock profile photos and posed as right-leaning individuals across the United States. Some of the removed accounts were older, and had pretended to be left-leaning individuals around the 2018 US congressional elections.
The overall effect was to sow political discord and undermine faith in the democratic process, just as Mueller's report last year said was Russia's overarching and continuing aim.
The most egregious example disclosed by Facebook involved a US marketing firm that used teenagers in Arizona to post comments that were either pro-Trump or sympathetic to conservative causes, while also criticizing 2020 Democratic candidate Joe Biden.
Research undertaken by Tucker and his colleagues shows that political partisanship -- heightened by social media algorithms that drive users to one side of a story -- means neither liberals or conservatives are good at sorting fact from fiction when challenged.
As part of a third-party fact-checking relationship with Facebook, AFP has flagged thousands of false or misleading posts in the US. Some had been shared hundreds of thousands of times. User feedback shows that even verified facts are not accepted when they go against partisan political belief.
Twitter is also removing impostor content. One such account featuring the image of a Black police officer, Trump and the slogan "VOTE REPUBLICAN" gained 24,000 followers earlier this month despite tweeting only eight times.
Its most popular tweet was liked 75,000 times before the account was removed for breaking the platform's rules against manipulation.
But social media researchers say the detection of such accounts are the exception rather than the norm.
From Pizzagate to QAnon
Professor Russell Muirhead, co-author of "A Lot Of People Are Saying," a title that plays on words often used by Trump to promote unproven theories, said US disinformation has evolved rapidly since 2016.
Referring to Pizzagate, the false claim that top Democrats ran a child sex trafficking ring from a Washington, DC pizza restaurant, Muirhead said political debate has been poisoned.
"This story, with no basis whatsoever, purports to show Hillary Clinton as a concentration of pure evil," said Muirhead, who teaches politics and political science at Dartmouth College.
"How do you make politics with such a person? You can't, so you have to make war. That story told Trump supporters that in a political context you are engaged in a war with someone who should be locked up."
In this election cycle, Pizzagate has metastasized and been succeeded by the QAnon conspiracy theory, which claims that Trump is locked in a struggle with Democratic and Hollywood elites who practice child sex trafficking and cannibalism.
Its adherents are taking aim at Biden.
"QAnon is now painting Joe Biden not as a legitimate opponent but as part of this team of globalists who are intent on destroying America, not to be argued with but to be eliminated," said Muirhead.
The most immediate disinformation risk to the 2020 vote, however, according to Tucker, is Trump’s repeated claims that the use of mail-in ballots will lead to fraud and a "rigged" election.
He made the same claims in 2016. Subsequent investigations showed no evidence of widespread fraud.
"This is disinformation," said the NYU's Tucker.
"There are problems with people not filling out their ballots correctly, there's problems with people getting their ballots late, but there is no evidence to suggest that there has been wide-scale fraud.
"Who needs the Russians running around casting doubt on the integrity of the democratic process when the president of the United States is doing it?"