Facebook and Twitter have each agreed to appear before U.S. lawmakers and testify publicly as part of a congressional probe into Russian interference during the 2016 presidential election.

Google has also been invited to testify at that hearing, scheduled before the Senate Intelligence Committee on November 1, but the search giant did not immediately comment on its plans Wednesday.

The rare appearance in front of one of the most powerful panels on Capitol Hill could prove to be a uniquely uncomfortable one for the country’s top technology companies. Facebook and Twitter, at least, are set to face tough questions -- for the first time, in the open — about the Russian-backed accounts and advertisers that took advantage of their platforms to spread misinformation ahead of Election Day.

For now, though, Facebook and Twitter have not yet shared whether their chief executives — Mark Zuckerberg and Jack Dorsey, respectively — would testify in front of Senate investigators.

"As we noted in our blog post last week, we are cooperating with these investigations in Russian interference in the 2016 election,” a Twitter spokeswoman said. “Twitter deeply respects the integrity of the election process, and will continue to both work with the investigations and to share details of our findings with the public as we are able."

Facebook also announced Wednesday it would testify at a second hearing to be convened by another panel that’s investigating Russian election interference, the House Intelligence Committee. Twitter and Google have not revealed their plans for that potential public grilling, which has been tentatively set for this month.

Since lawmakers began probing the matter, Facebook has uncovered roughly 470 profiles tied to Russian-backed sources. Those profiles purchased about 3,000 ads around the 2016 election in an attempt to stoke political unrest in the United States. Facebook estimates they were viewed by about 10 million users in the United States before and after Trump’s win.

Some of those profiles also had ties to approximately 200 accounts that Twitter discovered in its own review, which the company shared with Congress last week. Google, meanwhile, has not released any information about Kremlin activities on its advertising platform or other websites, like YouTube, though an investigation is ongoing.

For Senate investigators, the chief concerns are 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,” said Sen. Mark Warner, the top Democrat on the Intelligence Committee.

Warner had joined the panel’s leader, Chairman Richard Burr, at a press conference earlier Wednesday — and the duo warned that the United States remains at risk for future election interference by Russia and other malefactors.

“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,” said Burr, referring to an upcoming election in Warner’s own home state, Virginia, in the coming weeks.

To answer lawmakers’ questions, Facebook could choose to dispatch Chief Security Officer Alex Stamos, who has been spearheading the company’s internal hunt for ads and posts from Russia or other foreign actors. Twitter, meanwhile, might opt for Colin Crowell, its vice president for global public policy, who briefed House and Senate lawmakers last week.

But the executives they dispatch could be in for a gruesome grilling from lawmakers who believe Silicon Valley should have done more, and sooner, to combat Russian-sponsored disinformation on their sites. Even outside the investigation into the 2016 election, there are members of Congress calling louder than ever for more regulation of companies like Facebook and Twitter and the content that appears on their platforms.

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