The Senate Judiciary Committee holds a hearing Tuesday concerning extremist groups and Russian meddling in the U.S. political system through social media with, from left, Colin Stretch, Facebook’s general counsel; Sean Edgett, Twitter’s acting general counsel; and Richard Salgado, Google’s director of law enforcement and information security. (Melina Mara/The Washington Post)

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Lawmakers grilled executives of three leading tech companies Tuesday in a wide-ranging and sometimes contentious hearing that focused on the ability and willingness of Silicon Valley to combat ma­nipu­la­tion of U.S. elections by the Russians and other foreign actors.

The Senate hearing, the first of three to take place on Capitol Hill this week, represented a rare moment in the political spotlight for companies that, despite large lobbying teams in Washington, generally seek to avoid public scrutiny and potentially unpredictable confrontations. A growing number of lawmakers have vowed to expose Russian interference on U.S. technology platforms and work to prevent a recurrence through legislation.

The companies' testimony comes on the heels of revelations that the reach of the Russian-connected disinformation campaign on Facebook, Google, and Twitter was much larger than initially reported. As many as 126 million Facebook users may have seen content produced and circulated by Russian operatives. Twitter said it had discovered 2,752 accounts controlled by Russians, and more than 36,000 Russian bots tweeted 1.4 million times during the election. And Google disclosed for the first time that it had found 1,108 videos with 43 hours of content related to the Russian effort on YouTube. It also found $4,700 worth of Russian search and display ads.

With the threat of regulation looming, lawyers for the companies took pains to appear accommodating as they faced a host of questions about their businesses, their role in democratic societies, their efforts to be transparent and their ability to clamp down on malicious and nefarious content in past and future elections. They said that they were pouring significant new resources into combating foreign meddling but fell short of endorsing proposed legislation that would hold technology companies that publish political ads to the same disclosure standards as television and radio broadcasters.

“The foreign interference we saw is reprehensible,” Facebook General Counsel Colin Stretch said in his opening remarks. “That foreign actors, hiding behind safe accounts, abused our platform and other Internet services to try to sow division and discord — and to try to undermine the election — is an assault on democracy that is directly contrary to our values and violates everything Facebook stands for.”

Twitter acting general counsel Sean Edgett said that half the company’s approximately 3,000 employees were engaged in fighting abuse of its service. Facebook said it had about 150 employees fighting terrorism alone.

The lawmakers appeared skeptical. Some expressed frustration with the pace of revelations, with Sen. Christopher A. Coons (D-Del.) decrying the companies’ “slow, halting steps” to come forward and help lawmakers understand what took place.

The most tense exchanges took place when the companies were asked to explain more about what their services can and can’t do — and what capabilities they have to prevent abuse. Sen. John Neely Kennedy (R-La.) challenged Stretch with pointed questions.

“I’m trying to get us down from La-La Land here,” Kennedy said. “You have 5 million advertisers that change every year, every month, probably every second . . . You do not have the ability to know about every one of those advertisers, do you?”

When Stretch acknowledged that advertisers probably can obscure their identities, Kennedy interrupted him to ask pointedly, “Do you have a profile on me?” Then he asked whether Facebook knew the movies that his fellow senator Lindsey O. Graham (R-S.C.) liked, the bars he visited and who his friends were.

Stretch replied that Facebook has systems to prevent such invasions of privacy. “The answer is absolutely not. . . . We have designed our system to avoid exactly that.”

After Kennedy sharply reminded Stretch that he was under oath, Kennedy turned his attention to Google attorney Richard Salgado. The senator demanded to know whether the company was essentially a newspaper, rather than merely a neutral platform, given its role in distributing news reports worldwide. The issue has important consequences because under federal law, technology platforms do not have the same legal responsibility for material they carry as traditional news sources that employ journalists.

“We are not a newspaper. We are a platform that shares information,” said Salgado, Google’s director of law enforcement and information security.

Sen. Al Franken (D-Minn.) also took aim at Facebook, blasting the company for failing to discover the Russian online influence campaign sooner, especially given that many of the ads were paid for in rubles, the Russian currency. “American political ads and Russian money, rubles — how could you not connect those two dots!”

Stretch replied: “In hindsight, we should have had a broader lens. There were signals we missed.”

The most important unanswered question going into the hearing, experts said, is whether the tech companies have evidence that might substantiate allegations that the Russians colluded with President Trump’s political campaign, which made Facebook in particular a focus of its election efforts in 2016. Trump and his campaign officials have repeatedly denied allegations of collusion, but questions about the role played by Russia are at the heart of investigations on Capitol Hill and by special counsel Robert S. Mueller III, whose first charges against Trump campaign figures were unsealed Monday.

Intelligence agencies concluded in January that the Russian government engaged in a vast campaign to meddle in the presidential election and tilt the outcome toward Trump.

The hearing, as well as Wednesday’s hearings before the Senate and House Intelligence committees, comes amid pushes by Sens. Mark R. Warner (D-Va.), Amy Klobuchar (D-Minn.) and John McCain (R-Ariz.) to pass new legislation forcing tech companies to disclose information about political ads sold and distributed on their networks.

The bill, dubbed the "Honest Ads Act," would require digital platforms with more than 50 million monthly viewers to create a public database of political ads purchased by a person or group that spends more than $500. The public file would include the ad, a description of the targeted audience, the number of views it generated, the date and time it ran, its price, and contact information for the purchaser.

The companies have tried to get ahead of the bill by introducing their own transparency initiatives. Facebook, and then Twitter and Google, have vowed to publish all federal election-related ads that name a candidate in a public database, as well as the amounts spent on those ads.

But when asked by Klobuchar whether they would support the bill, the executives avoided a direct answer.

“We certainly support the goals of the legislation and would like to work through the nuances,” Salgado said.

“We’re not waiting for legislation. . . . We stand ready to work with you,” Stretch said.

“The same goes for Twitter,” Edgett said.

In an interview after the hearing, Klobuchar said she was disappointed that the tech companies declined to support the ad transparency bill.

“They’ve been willing to expose a major problem, but they are still opposing a national solution,” she said.

“We are only 370 days away from the next federal election. And we can’t just keep dialoguing about this anymore.”