This week, Mr. Warner, the top Democrat on the Senate Intelligence Committee, will push for new answers. Executives from Facebook, Google and Twitter are set to testify at congressional hearings on Tuesday and Wednesday about the election and the power of their platforms.
Lawmakers are increasingly taking a critical tone with Silicon Valley, with Mr. Warner among the harshest. He has already pushed a bill requiring the companies to disclose who paid for digital political ads, the biggest legislative effort so far to regulate the companies.
Mr. Warner’s position is a sharp reversal. Before entering politics, he built a fortune that at one time was estimated at around $200 million as a technology and telecommunications investor and executive. His political identity, first as governor of Virginia and then as a senator, has been wrapped in promises to bring 21st century jobs. He has a broad and close network of tech executives and investors.
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Al Drago for The New York Times
Mr. Warner is emblematic of the shifting politics for technology.
“Mark didn’t come to this point with the social media companies lightly,” said Saxby Chambliss, a retired Republican senator from Georgia who regularly meets with Mr. Warner and the Intelligence Committee chairman, Senator Richard Burr of North Carolina, a Republican, to discuss the Russia investigation.
The reluctance of the technology companies to take seriously the investigation into Russian election meddling pushed Mr. Warner over the edge, Mr. Chambliss said.
“That is a poor attitude for American companies,” Mr. Chambliss added. “Mark will make sure this issue is highlighted because it needs to stop.”
Ahead of the hearings, Twitter and Facebook have scrambled to disarm lawmakers with announcements of voluntary changes to their advertising businesses. Sheryl Sandberg of Facebook, for example, spent a couple days in Washington promising more disclosures. Twitter announced it would disclose who buys political ads on its site, and it blocked two Russia-based media organizations from purchasing advertisements.
“Twitter is taking an appropriate and welcome step,” Representative Adam Schiff of California, the leading Democrat on the House Intelligence Committee, said last week.
The companies say the internal investigations and answering lawmakers’ questions are a top priority. In their announcements on voluntary ad disclosures, Twitter and Facebook said their stricter policies for who can place political ads and promises to make those purchases public are signs of their commitment to correcting their mistakes.
“We look forward to answering lawmakers’ questions,” said Joel Kaplan, vice president of global public policy for Facebook, in a statement. “We take this issue very seriously and think it’s important Congress gets the full picture of what happened, including what we know about Russian activity on our platform, and is able to share its assessment with the American public.”
But lawmakers said the companies, who have been interacting privately for months, still have a long way to go.
Last week, congressional aides said the online giants were pushing back against lawmakers. The companies argued against the ad disclosure bill and dragged their feet to participate in a hearing on Tuesday. Lobbyists for Facebook explained how their voluntary efforts on political ad disclosures could work better than regulations.
Twitter has not addressed its problems with automated accounts, known as bots, that can quickly spread propaganda or fake news. In addition, not all social media companies have announced that they will tighten rules for buying political ads, one of the most pressing issues. And even if they do, lawmakers should still make more disclosure a legal requirement, said Senator Amy Klobuchar, Democrat from Minnesota, who is a co-sponsor of the disclosure bill with Mr. Warner and Senator John McCain, Republican of Arizona.
“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.
Much of the harshest criticism so far is coming from Democrats like Mr. Warner and Ms. Klobuchar, which could limit the fallout for the tech companies. The Republican chairman of the Senate Intelligence Committee, Mr. Burr, has been more reserved than Mr. Warner, for example.
Many Republicans are reluctant to add any regulations to businesses. Some are also afraid of crossing other party members or President Trump, who regularly play down Russian interference in the election.
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Christie Hemm Klok for The New York Times
Republicans have slowly begun calling for more scrutiny of the companies. But lawmakers who are more oriented toward free markets have been reluctant to regulate the rapidly evolving industry. Other top regulators, particularly those appointed by Mr. Trump, are also considered unlikely to take strong action against the industry.
The top antitrust enforcer at the Justice Department, Makan Delrahim, said in an interview last week that his agency would watch to see whether the size of technology companies hurts competition, but that size alone was not justification for action against them.
“There are people who think big is just bad,” Mr. Delrahim said. He invoked the name of Robert Jackson, the top antitrust enforcer for the agency about 80 years ago, who said he was reluctant to try to break up big companies just for the sake of doing so.
That has made it easier for Mr. Warner to assert himself as a leading voice about the power of the tech companies — as unexpected as it may be.
Mr. Warner accumulated his wealth with an early investment in the cellular service provider Nextel, which was sold to Sprint in 2005 for $35 billion. Mr. Warner then became a start-up investor at Columbia Capital, which had an office in Alexandria, Va. He used his fortune to run for governor of Virginia, talking on the campaign trail about bringing work force training and tech-oriented economic development to rural parts of the state. After serving a term, he was elected to the Senate in 2008.
And even with his recent criticism of the industry, he regularly taps a broad network of tech executives and investors for counsel.
During the summer, Steve Case, the founder of AOL, stayed at Mr. Warner’s vacation home on Martha’s Vineyard. For years, the two have met regularly to talk about techology-related policy issues, like how artificial intelligence could alter the future of labor.
But during this year’s trip, they discussed the Senate intelligence committee’s Russia investigation and the power of social media platforms and their role in the election.
“His thinking has evolved,” Mr. Case said. “Even though I’m sure this has some benefit with his profile, all things being equal, I think he has approached this with some reluctance because he’d rather be focused on issues like the future of work.”
And Mr. Warner sees no contradiction in his evolution to being considered a sharp prod of Silicon Valley.
“Look, I’m pro-tech. I’m pro-innovation,” he said, standing and shuffling side to side like a basketball player on defense. On the bookshelf near him was a textbook, “Science and Engineering,” and a small business self-help book called “Grow Regardless: Of Your Business’s Size, Your Industry or the Economy … and Despite the Government!”
He went on: “What I fear is 2018. If you look at Russian intervention in the American elections, in terms of sowing chaos, they had pretty good R.O.I.,” he said, pulling from his past life with the business acronym for return on investment.
“There is too much at stake,” he said.
