But American intelligence agencies have concluded that President Vladimir V. Putin of Russia tried to sway the election in favor of President Trump, beyond just posting disruptive content on social media. Russian operatives also hacked Democratic email accounts and released messages embarrassing to Hillary Clinton’s campaign.
Senator Lindsey Graham, Republican of South Carolina and chairman of the subcommittee, asked Facebook to confirm a narrower point — that the pattern of activity it saw from Russia was more focused on sowing chaos in the United States than in bolstering Mr. Trump’s candidacy.
“During the election, they were trying to create discord between Americans, most of it directed against Clinton,” Mr. Graham said, addressing Facebook’s general counsel, Colin Stretch. “After the election, you saw Russian-tied groups and organizations trying to undermine President Trump’s legitimacy. Is that what you saw on Facebook?”
Mr. Stretch agreed.
Google tries to distance itself from Facebook and Twitter.
In his opening remarks, Richard Salgado, Google’s senior counsel of law enforcement and information security, walked a tightrope. He said that the company was taking the threat of government-backed interference seriously, but noted that Google’s array of services functioned differently than its social media peers, Facebook and Twitter.
He said while Russian agents used YouTube, owned by Google, to upload political videos, it gained momentum because of social media platforms.
“We did observe that links to these videos were frequently posted to other social media platforms,” he said. “We believe that the relatively limited amount of activity we found is a result of the safeguards we had in place in advance of the election.” He added, “Google’s products also don’t lend themselves to the kind of targeting or viral dissemination these actors seem to prefer.”
The distinction is one that Google has made privately, and it is more an accident of history — because Google’s social media efforts have largely failed — than an intentional strategy by the company.
The problem was worse than reported.
Facebook, Twitter and Google have been slow to acknowledge their significance in the Russian influence campaign. Right after the election, Facebook’s chief executive, Mark Zuckerberg, scoffed at the idea that fake news on the site could have swayed public opinion before the election.
It took months for the companies to begin their own investigations. In late September, Senator Mark Warner of Virginia, the top Democrat on the Senate Intelligence Committee, said that information provided by Twitter and Facebook seemed to greatly underplay their problems.
On Monday, the companies acknowledged the problem was much bigger.
In prepared remarks, Facebook said inflammatory posts by Russian agents intending to sow discord among Americans reached 126 million users. Google said that the same agents, from the Kremlin-linked Internet Research Agency, uploaded over 1,000 videos on YouTube. Twitter said they published more 131,000 messages on Twitter.
And the companies also acknowledged they were wading into new territory.
“The abuse of our platform by sophisticated foreign actors to attempt state-sponsored manipulation of elections is a new challenge for us — and one that we are determined to meet,” Twitter’s acting general counsel, Sean Edgett, said in written testimony.
Mr. Stretch said in written testimony, “The foreign interference we saw is reprehensible and outrageous and opened a new battleground for our company, our industry, and our society.”
The companies stressed that over all, content connected to the Russian company was a sliver of all that they publish each day.
But the new information will only raise more questions: How long did they know of the activity? How far back have they investigated the activity of these accounts? Beyond the Internet Research Agency, were there similar efforts by other foreign-linked companies?
Lawmakers want more tech regulations.
The political winds have shifted for Silicon Valley, with a growing number of legislators sounding alarms in recent months over the power that Facebook, Google and Twitter have over public opinion.
Some lawmakers are now proposing to rein them in by regulating political ads on their digital platforms. After Facebook disclosed in September that it had identified more than $100,000 in advertisements paid for by the Internet Research Agency, lawmakers proposed legislation that would ask websites to submit to the same sort of disclosures rules imposed on broadcast television.
Senator Sheldon Whitehouse, Democrat of Rhode Island, called for the companies to explain what efforts they were making to ensure the same mistakes were not repeated.
“Can you come to us and say, ‘We have accomplished X, and therefore you, as a Congress, don’t need to worry about legislating in this space or creating regulations or holding more hearings, because we have now got America’s back?’ Can you do that for me?” he asked.
Senator Amy Klobuchar, Democrat of Minnesota, was also expected to make a strong push for a bill that required sites like Facebook and YouTube to disclose the sources of funding for political ads. She recently introduced the legislation with Senator John McCain, Republican of Arizona, and Mr. Warner.
Ahead of the hearing, Facebook and Twitter announced they would voluntarily disclose the sources of funding behind political ads. Twitter went further to ban ads from two Kremlin-backed news outlets as well as vowing to disclose the source of funding for all ads.
But lawmakers say self-regulations won’t cut it.
“If their policies comply with our bill, they should support our bill and maybe can use their policy as a standard when we pass our bill,” Ms. Klobuchar said in a recent interview.
It’s not just about ads.
Political ads are just part of the problem. Russian agents also spread nonpaid content through the creation of pages on Facebook dedicated to hot-button issues like race. On Twitter, the Internet Research Agency used automatic messaging tools known as bots that could quickly spread tweets through multiple accounts.
Lawmakers are pressing the companies on what they’ve done to to fight misinformation on “organic posts” and bots.
“They’re using our own social networks, our friendships, families and biases and viewpoints against us,” Mr. Whitehouse said.
Another problem is issues-oriented ads that are not defined as political ads because they do not directly promote a political candidate. Such ads would include an environmental group publishing an ad attacking environmental deregulation or anti-immigration groups calling for stricter border policies.
“I have a particular concern about issue advertisements, sock puppets, and the dissemination of made-up stories, tactics we know Russia and other actors have used extensively,” Senator Ron Wyden, Democrat of Oregon, said in a statement before a Senate Intelligence Committee hearing on Wednesday with the same executives from Facebook, Google and Twitter. The House Intelligence Committee also has a hearing scheduled.
Republicans are pressing tech companies, too.
Republican lawmakers are also beginning to criticize the Silicon Valley companies. This is important because any call for regulations by Republican lawmakers, who tend to be free-market-oriented, make the long-shot risk of tech legislation more plausible.
In one contentious exchange, Senator John Kennedy, Republican of Louisiana, pressed Mr. Stretch on whether Facebook could possibly have oversight of all of its advertisers.
“I’m trying to get us down from la la land here,” Mr. Kennedy said. “The truth of the matter is, you have 5 million advertisers that change every month. Every minute. Probably every second. You don’t have the ability to know who every one of those advertisers is, do you?”
Mr. Stretch acknowledged Mr. Kennedy’s point.