Congressional investigators who are studying Russia’s attempts to influence the 2016 U.S. presidential election are still missing a key tranche of evidence: The posts and other content penned by Kremlin-tied accounts on Facebook.

Earlier this month, the social giant fulfilled its pledge to turn over to the House and Senate Intelligence Committees a copy of roughly 3,000 advertisements purchased by 470 Russian-backed accounts identified on its platform. Many of those ads sought to stoke racial, religious and other social political tensions in a bid to cause political unrest in the United States, sources have said.

But those advertisements also linked back to specific Facebook profiles and pages — hubs like the gun-glorifying page Defend the 2nd, as reported by publications like The New York Times, as well as others targeting gay rights and groups like Black Lives Matter. And those since-deleted profiles and pages contained a full trove of content — posts that were written or shared, but not necessarily promoted -- that hasn’t actually been provided in full with congressional leaders, according to sources familiar with the matter.

Silicon Valley’s Russia ads problem, explained The Recode guide to what Facebook, Google and Twitter have found on their sites, and how the U.S. government is responding.

That body of data is crucial. Facebook on its own has revealed that approximately 10 million U.S. users saw the 3,000 Russian bought ads before and after Election Day. But it is not clear how far and wide those same accounts’ free posts — what normally might be described as organic — have spread on the platform.

For now, at least one study — first reported by The Washington Post earlier this week — has found that just six of the profiles flagged by Facebook for their ties to the Kremlin had their free content shared 340 million times. In that report, “share” is defined as content that appeared in users’ news feeds, not whether users actually interacted with it.

Asked about the data it’s provided to federal lawmakers, a spokesman for Facebook declined comment. But the aide did point Recode to the company’s previous blog post from September 21, which said Facebook would turn over the “content of these ads, along with related information, to congressional investigators.”

A spokeswoman for Sen. Richard Burr, the leader of the Senate Intelligence Committee, did not respond to requests for comment. A spokeswoman for the panel’s top Democrat, Sen. Mark Warner, declined comment. House lawmakers did not respond to emailed questions Friday.

For now, the Senate panel along with its House counterpart are reviewing the information they’ve already obtained from Facebook as well as its tech peers, Google and Twitter, ahead of two scheduled hearings on social media and the 2016 presidential election. Facebook and Twitter have confirmed they plan to testify at those back-to-back sessions, slated for November 1, but Google has not commented on its attendance.

To Warner, at least, a key concern entering the hearing is the extent to which Russian forces purchased ads and created false accounts “that would drive interest toward stories or groups,” with the goal to “sow chaos and drive division in our country,” he said at a press conference earlier this week.

And Burr, for his part, has emphasized the United States is still vulnerable to election interference. “The Russian intelligence service is determined, clever, and I recommend every campaign and every election official take this very seriously as we move into this November’s election,” the Republican chairman said.

Obtaining the missing data directly from Facebook could be crucial for congressional lawmakers probing the extent of Russia’s 2016 election meddling.

The company already has shut down the 470 accounts linked to the Internet Research Agency, a Kremlin-backed online troll farm. And while lawmakers and their aides might be able to obtain the contents of those profiles and pages using some of the web’s archive tools, much as some reporters have done, Facebook could make it much easier on Congress by providing the data in full.

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