All of a sudden, Facebook—and perhaps Twitter and Google, too—find themselves at the center of the Russiagate investigation.

You can’t say you didn’t see this coming. Back in January, in its Intelligence Community Assessment on Russia’s attack on the 2016 US election, the American Intelligence Community told us that a critical part of the Moscow-directed effort involved “paid social media users or ‘trolls.’” That attack, which the ICA said was directed personally by President Vladimir Putin, was a “multifaceted” campaign that went far beyond the well-known reports that Russia’s agents hacked into, or obtained through spearphishing, the e-mail accounts of the Democratic National Committee and John Podesta.

In an assessment that resonates with the latest disclosures about Russian involvement with Facebook, Twitter, and other social-media platforms, the ICA noted that the Russians “used trolls as well as RT [the media organization formerly known as Russia Today],” in tandem with the secretive work of an outfit called the Internet Research Agency. And, it added, “The likely financier of the so-called Internet Research Agency of professional trolls located in Saint Petersburg is a close Putin ally with ties to Russian intelligence.”

It’s taken a while for the facts to emerge about how the Russian intelligence services, using a vast army of Internet trolls and “bots,” intervened in the 2016 contest. Robert Mueller, the special counsel named by the Justice Department to look into Russiagate, has demanded that Facebook come clean on what it knows about improper and possibly illegal Russian efforts to use Facebook last year. And Facebook itself, which at first stonewalled congressional investigators, has no choice—faced with subpoenas and search warrants—but to grudgingly tell Mueller what it knows.

For Facebook, and for Mark Zuckerberg, it’s been a halting journey to reveal the extent of Russian meddling across its billion-member platform. After first resisting the notion that Russia, or anyone, could use Facebook in an effort to manipulate the election, calling it “a pretty crazy idea,” Zuckerberg issued a lengthy Facebook Live statement late last week. “I don’t want anyone to use our tools to undermine democracy,” he said, describing a series of nine steps that he’s ordered the Internet behemoth to undertake to minimize the risk in the future. And he concluded, “We will continue working with the government to understand the full extent of Russian interference.”

There’s a long backstory that led to Zuckerberg’s statement. The first glimpse at how Russia might have used Facebook in 2016 appeared this past spring in a Time magazine piece, “Inside Russia’s Social Media War on America,” by reporter Massimo Calabresi. He reported: “Intelligence officials have found that Moscow’s agents bought ads on Facebook to target specific populations with propaganda. ‘They buy the ads, where it says sponsored by—they do that just as much as anybody else does,’ says the senior intelligence official. (A Facebook official says the company has no evidence of that occurring.)”

In fact, Facebook did indeed have evidence that such interference occurred, and it went far beyond simple advertising. In a September 6, 2017, blog posting by Alex Stamos, Facebook’s chief security officer, the company admitted it had indeed uncovered some skulduggery. “In reviewing the ads buys, we have found approximately $100,000 in ad spending from June of 2015 to May of 2017—associated with roughly 3,000 ads—that was connected to about 470 inauthentic accounts and Pages in violation of our policies. Our analysis suggests these accounts and Pages were affiliated with one another and likely operated out of Russia.” The ads and fake accounts, said Stamos, “appeared to focus on amplifying divisive social and political messages across the ideological spectrum—touching on topics from LGBT matters to race issues to immigration to gun rights.”

But even that belated Facebook admission understates the size and scope of the Russia-based intervention. According to investigative reports across a wide range of American newspapers, television outlets, and websites, the full scope of what Russian operatives did, or tried to do, is just beginning to emerge. Mark Warner, the ranking Democrat on the Senate Intelligence Committee, says that what we know now is only “the tip of the iceberg.” And the ongoing investigations may show that Russian use of Facebook in the United States last year went far beyond 470 “inauthentic accounts.” In April, the company acknowledged that it had suspended 30,000 fake accounts during France’s recent presidential election. And Zuckerberg last week revealed that his company was taking action against thousands of fake accounts during this month’s German election campaign. In neither case, though, were all of the accounts necessarily linked to Russian involvement

In fact, the Russians operated a vast “troll farm” that used social media in 2016, creating, for instance, fake Facebook users that looked, sounded like (sort of), and acted like plain old American folks from the heartland. In one case, they tried to organize a coterie of right-wing, anti-immigrant activists to attend a rally in, of all places, Idaho.

According to a September Daily Beast exclusive, later confirmed by Facebook, “Russian operatives hiding behind false identities” sought to promote an Islamophobic, anti-immigrant demonstration in Twin Falls, Idaho, in August 2016. The Russians created a Facebook event page, with rhetoric such as: “We must stop taking in Muslim refugees! We demand open and thorough investigation of all the cases regarding Muslim refugees! All government officials, who are covering up for these criminals, should be fired!” According to The Daily Beast, the fake event, organized by a false-flag Russian front called SecuredBorders, was promoted by an ersatz page that claimed up to 133,000 Facebook followers. (It should be noted that during that period, far-right, pro-Trump sites such as Breitbart and Alex Jones’s Infowars had already been trying to whip up anti-Muslim sentiment in Idaho, complete with reckless stories about supposed Muslim rapists and a plague of immigrant-caused “tuberculosis in Twin Falls.”) The Idaho Statesman, in reporting Facebook’s admission that all this happened, also carried a screenshot of the SecuredBorders page, “Citizens before refugees.”

One pro-Trump Facebook page, which according to The Daily Beast is also suspected of having been set up by Russian propagandists, called itself “Being Patriotic” and promoted a flash-mob rally in 17 Florida cities in August 2016 under the title “Florida Goes Trump!”

For its part, Moscow denies putting ads on Facebook. “We do not know…how to place an advert on Facebook. We have never done this, and the Russian side has never been involved in it,” said Dmitry Peskov, the Kremlin spokesman, to reporters. Echoing Moscow’s denial of its involvement, and ignoring Facebook’s statements, on September 22 President Trump tweeted his ridicule. “The Russia hoax continues, now it’s ads on Facebook.”

But, as The New York Times, The Washington Post, and other outlets have reported, the Russian use of Facebook, Twitter, et al. was troubling, if not particularly large by Facebook or ad-campaign standards. In one example, reported by the Times, a false persona calling itself “Melvin Redick” of Harrisburg, Pennsylvania, used stolen photos of a man in Brazil who appeared to be “a friendly-looking American with a backward baseball cap and a young daughter.” This nonexistent person turned out, according to the Times, to be “among the first public signs of an unprecedented foreign intervention in American democracy.” In his posts, “Redick” pointed to a just-launched website called DCLeaks—the very website that US officials say was created by Russia’s military-intelligence service, the GRU, and that was among the sites that revealed the hacked DNC e-mails—and said, “These guys show hidden truth about Hillary Clinton, George Soros and other leaders of the US. Visit #DCLeaks website. It’s really interesting!” Yes, really interesting.

The Times, in its report, added: “On Twitter, as on Facebook, Russian fingerprints are on hundreds or thousands of fake accounts that regularly posted anti-Clinton messages. Many were automated Twitter accounts, called bots, that sometimes fired off identical messages seconds apart—and in the exact alphabetical order of their made-up names, according to the FireEye researchers. On Election Day, for instance, they found that one group of Twitter bots sent out the hashtag #WarAgainstDemocrats more than 1,700 times.”

The Washington Post, in its report earlier this month on the Russia-Facebook connection, quoted an unnamed Facebook official: “There is evidence that some of the accounts are linked to a troll farm in St. Petersburg, referred to as the Internet Research Agency, though we have no way to independently confirm.” A troll farm is a kind of assembly line of employees hired to sit side by side in large numbers to post a seemingly unending stream of comments, Facebook posts, tweets, Instagram photos, and other messages on behalf of their employer.

The St. Petersburg–based Internet Research Agency, one of the alleged culprits behind the 2016 Russia-Facebook operation, was the subject of a lengthy and fascinating report by Adrian Chen in The New York Times Magazine way back in 2015. Long before the Russian election intervention of 2016, the Times report provided a stunning—if mostly overlooked—glimpse into the work of Russia’s Internet trolls, based on deep reporting and interviews with former members of the troll force.

In his must-read investigative report, Chen describes a series of hoaxes and alarmist reports organized and fostered by the agency, and his conclusion was more than prescient. “The agency had become known for employing hundreds of Russians to post pro-Kremlin propaganda online under fake identities, including on Twitter, in order to create the illusion of a massive army of supporters; it has often been called a ‘troll farm.’ The more I investigated this group, the more links I discovered between it and the hoaxes,” he wrote. “Russia’s information war might be thought of as the biggest trolling operation in history, and its target is nothing less than the utility of the Internet as a democratic space.”

Back then, the focus of the Internet Research Agency was mostly Ukraine and domestic Russian politics—i.e., trolling Russia’s domestic political opposition. But as we’ve since learned, the agency took an important role, though perhaps not even the leading one, in Russia’s intervention in the 2016 US election.

On September 15, The Wall Street Journal reported that Mueller, the special counsel, using the power of court-ordered search warrants and grand jury-backed subpoenas, has demanded Facebook’s full cooperation in his probe, and Facebook appears to be cooperating, says the Journal. “The information Facebook shared with Mr. Mueller included copies of the ads and details about the accounts that bought them and the targeting criteria they used, the people familiar with the matter said,” it reported.

And, after first resisting full cooperation with parallel investigations by the House and Senate intelligence committees, Facebook announced last Thursday that it would turn over to both committees copies of more than 3,000 ads purchased through Russian accounts during the 2016 campaign.

Meanwhile, Congress isn’t letting go. Representative Adam Schiff, the ranking Democrat on the House Permanent Select Committee on Intelligence, cheered Facebook’s reluctant decision to work with his committee, but added that he intends to include Twitter, Google, and others as the inquiry expands. “The data Facebook will now turn over to the committee should help us better understand what happened, beyond the preliminary briefings we already received. It will be important for the committee to scrutinize how rigorous Facebook’s internal investigation has been, to test its conclusions and to understand why it took as long as it did to discover the Russian-sponsored advertisements and what else may yet be uncovered,” he said.

“As we continue our investigation to get to the bottom of Russia’s multifaceted attack on our democratic process,” he concluded, “I believe it will be necessary to hear directly from Facebook, Google, and Twitter, as well as others in the tech sector, including in open hearings that will inform the American public.”

Renato Mariotti, a former federal prosecutor writing in Newsweek, says the news about Russia’s use of Facebook may signal a “turning point.”

“Mueller’s warrant tells us that the special counsel is closing in on specific foreigners who tried to undermine our democracy, that he’s serious about going after Russian interference and he is far enough along to convince a federal judge that he has good evidence of such a crime,” wrote Mariotti. “Mueller’s warrant has the potential to profoundly change this investigation—as well as its fallout.”