WASHINGTON — Angry senators warned attorneys for Facebook, Twitter and Google on Wednesday that they must do more to prevent Russian manipulation of their social media platforms or Congress will be forced to impose new rules to help readers identify malicious content.

"I must say, I don't think you get it," Sen. Dianne Feinstein, D-Calif., told the attorneys at a hearing before the Senate Intelligence Committee focused on Russian interference in the 2016 presidential election. "What we're talking about is a cataclysmic change. What we're talking about is the beginning of cyber warfare...You have a huge problem on your hands."

"You created these platforms, and now they are being misused," Feinstein continued. "You have to be the ones to do something about it, or we will."

The Republican-led Congress has generally been reluctant to pass new regulations governing the private sector. However, congressional hearings with the social media companies on Tuesday and Wednesday showed that the hands-off approach may be changing amid growing frustration by lawmakers with the companies' response to Russian efforts to sow division and discontent among U.S. voters.

Also on Wednesday, Democrats on the House Intelligence Committee publicly released a sampling of ads and other content that Facebook, Instagram and Twitter have linked to Russian actors and turned over to the committee. The ads released Wednesday focus on such issues as the black lives matter movement, illegal immigration, Islam, LGBT issues, Christianity, state pride, and Democratic presidential candidates Hillary Clinton and Bernie Sanders — hot button topics apparently intended to instigate conflict.

The full House Intelligence Committee is still working with Facebook to release more than 3,000 ads purchased by the Kremlin-linked Internet Research Agency. The information must first be scrubbed of any personally identifiable data before being made public, Democrats said.

The panel's Democrats also released Twitter accounts identified by the company as connected to the Internet Research Agency, a Russian group with ties to the Kremlin that impersonates U.S. news organizations, political parties, and various interest groups.

Rep. Adam Schiff of California, the senior Democrat on the House committee, said it's clear that the Russians used social media to help the Trump campaign.

"Whether the Russians and Trump coordinated these efforts, we do not yet know, but it is true that the Russians mounted what could be described as an independent expenditure campaign on Trump’s behalf," Schiff said. "Russian ads on Twitter, for example, promoted stories about Hillary Clinton’s allegedly poor health or legal problems."

President Trump has repeatedly denied any collusion between his campaign and the Russians.

At the Senate Intelligence Committee hearing Wednesday morning, Chairman Richard Burr displayed posters of ads by two fake Texas groups that were posted on Facebook last year. One group pretended to be an anti-immigrant group and the second pretended to be a pro-Muslim group. Those ads, which were later found to be paid for by the Russians, spurred real protests from Americans who clashed in Houston.

"You must do better to protect the American people and frankly all of your users," said Burr, R-N.C.

Members of Congress have introduced the bipartisan "Honest Ads Act" in both the House and Senate that would require social media companies to disclose who is paying for political ads on their sites the way that traditional media companies already must do.

Companies also would be required to take "reasonable efforts" to ensure that foreign nationals are not purchasing political advertising. Federal election law prohibits foreign nationals from contributing to U.S. campaigns or buying election-related ads.

Social media companies have generally resisted such efforts, pledging to do a better job on their own of weeding out disinformation and foreign "bad actors" on their platforms.

Sean Edgett, Twitter's acting general counsel, said Wednesday that Twitter is "very supportive of the direction" that the Honest Ads Act is going, although he quickly added that the bill needs "fine-tuning." He also said Twitter is already acting voluntarily to do much of what the bill would mandate.

Kent Walker, Google's senior vice president and general counsel, said the company is committed to working with Congress and law enforcement to stop manipulation of its sites by foreign governments.

He said Google is using fact-check labels to help users spot fake news and has strengthened its advertising guidelines to confirm the identity of buyers and to let the public see who is sponsoring political ads. Facebook and Twitter are taking similar actions.

"Google believes that we have a responsibility to prevent the misuse of our platforms, and we take the responsibility seriously," Walker said.

Vice Chairman Mark Warner, D-Va., a former tech entrepreneur, said it "frankly strains credibility" that the social media companies had no idea that Russia was placing ads and spreading disinformation on their sites during the 2016 election cycle until Congress pressed them about it. Facebook and other companies initially dismissed the idea that Russians were manipulating their platforms.

When the companies did begin to acknowledge the problem last summer, their initial presentations to Congress were "less than sufficient," Warner said.

"They showed a lack of resources, a lack of effort and a lack of genuine commitment," Warner said.

The attorneys for the three companies all promised to continue working closely with the committee to strengthen their efforts.

Warner asked whether Facebook cross-checked 30,000 Kremlin-linked accounts that they took down during the French elections last spring to see if any of those accounts were also active during the 2016 U.S. presidential election.

When Facebook general counsel Colin Stretch said he'd have to get back to Warner with an answer, the senator erupted.

"We've had this hearing scheduled for months," Warner said. "I find your answer very, very disappointing."

Warner also asked Twitter why it took them so long to take down a fake account pretending to be the Tennessee Republican Party even after legitimate party officials asked them to do so. The fake account was later linked to a Russian group.

"That was an absolute miss," Edgett acknowledged.

The attorneys for Facebook, Google and Twitter testified Wednesday afternoon before the House Intelligence Committee after appearing before the Senate Intelligence Committee. They testified Tuesday before the Senate Judiciary Committee.

The three committees questioning the attorneys are all investigating Russian interference in the 2016 presidential election and possible collusion between the Trump campaign and Russian officials.

They also are trying to prevent Russian meddling from happening again in the 2018 congressional elections and beyond. The three attorneys acknowledged to the House Intelligence Committee on Wednesday that it's possible that groups linked to Russian intelligence officials are continuing to manipulate their social media platforms.

The hearings come amid revelations by Facebook this week that as many as 126 million people may have seen political material posted by a Russian troll farm using fake Facebook identities between 2015 and 2017. That is the largest estimate yet of just how widespread Russian manipulation of Facebook was.

On Wednesday, Stretch said that an additional 16 million people saw the Kremlin-linked material on Instagram, which is owned by Facebook.

Facebook disclosed in September that it had identified more than $100,000 worth of political ads purchased by a Russian company linked to the Kremlin. Most of the 3,000 ads, which ran between June 2015 and May 2017, focused on divisive issues such as immigration, gun control, gay rights and race.

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