Facebook Inc. hasn’t been “fully forthcoming” as Congress probed Russia’s attempted meddling in the 2016 presidential election, U.S. Senator Mark Warner of Virginia said today as the social-media giant faced continued fallout from an ongoing data crisis.

Warner, the top Democrat on the Senate Intelligence Committee, said on NBC’s “Meet the Press” that he questioned “the use of this really sketchy firm Cambridge Analytica,” but Facebook “blew that off” as they did other concerns over Russia’s actions.

The political firm, which consulted on President Donald Trump’s campaign, siphoned data from some 50 million Facebook users as it built an election-consulting company that boasted it could sway voters in contests all over the world. Facebook also came under scrutiny last year after the revelation that Russians had used the site in its attempts to affect the 2016 election.

The revelation of Cambridge Analytica’s action has caused days of fury for Facebook and its co-founder and chief executive officer, Mark Zuckerberg. Two congressional committees have invited Zuckerberg to testify, and he has said he’d agree if he is the right person to appear.

“The whole industry has been reluctant to accept the fact that we’re seeing the dark underbelly of social media — how it can be manipulated,” Warner said. “We’re still dealing right now with kind of fake posts and fake accounts.”

Facebook took out ads in multiple newspapers today apologizing for the events, which it called a “breach.”

Warner also said the U.S. should reexamine the claim, which is largely reflected in U.S. law, that social media sites “have no responsibility for any of the content,” and Warner added “maybe you should be able to move all your data” when moving between sites.

On March 21, a bill to limit a website’s immunity for content when it knowingly facilitates sex trafficking passed Congress — one of the first impositions of liability for online platforms as the U.S. debates their responsibility for what users post. Trump is expected to sign it into law.

Warner repeated his call for Zuckerberg to testify.

“He is the face of Facebook,” Warner said. “He in fact created this industry, and he needs to come explain to the American public and to policy makers.”

Zuckerberg should “explain how they’re going to work with us,” Warner said in a separate interview on CBS’s “Face the Nation.”

Facebook general counsel Colin Stretch was called before Congress last year, and Warner has said he now wants to hear testimony from Twitter Inc. CEO Jack Dorsey.

After last year’s hearings, Zuckerberg promised a “major ads transparency effort,” including requiring political advertisers to include a disclosure of their identities. Warner has said he wants Facebook to go further. The senator has pressed tech companies for more information about Russian meddling in U.S. elections, and called on them to harden their networks.

Questions remain about how Russia used Facebook to sway the 2016 U.S. presidential campaign. An indictment by special counsel Robert Mueller described a multiyear effort by the Internet Research Agency, a Russian outfit, and others to shape American opinions, including by impersonating Americans on Facebook, Instagram, Google’s YouTube and Twitter. About 150 million users saw posts from a St. Petersburg-based troll farm whose main purpose was to push Kremlin propaganda.

In addition to congressional probes, the U.S. Federal Trade Commission is scrutinizing whether Facebook violated a 2011 consent decree with its handling of personal user data that was transferred to Cambridge Analytica without users’ knowledge, according to two people familiar with the matter. It is also facing a probe in the U.K.