Mark Zuckerberg apologized for the data debacle that has upended Facebook and left the door open to testifying before Congress.

Mark Zuckerberg

“What we try to do is send the person at Facebook who will have the most knowledge,” Zuckerberg said. “If that’s me, then I am happy to go.”

Although Facebook employs a small army of lawyers and lobbyists in Washington, Zuckerberg himself has never testified before a congressional committee, according to a C-SPAN database.

Lawmakers want to change that. Politicians on both sides of the Atlantic have called for Zuckerberg to testify before their legislative bodies in the five days since the Cambridge Analytica scandal erupted.

The data firm, which has ties to President Donald Trump’s campaign, reportedly accessed information from about 50 million Facebook users without their knowledge.

Facebook says the data was initially collected by a professor for academic purposes in line with its rules. The information was later transferred to third parties, including Cambridge Analytica, in violation of Facebook’s policies, Facebook has said.

Zuckerberg broke his silence on the issue earlier Wednesday with a post on his personal Facebook page laying out a series of steps the company would take to better protect user data. But that wasn’t enough to appease lawmakers.

“The steps Facebook has laid out to protect its users are a start but Zuckerberg still needs to come testify,” Sen. Amy Klobuchar, a Democrat from Minnesota, wrote on Twitter Wednesday. She also urged the company to support new regulation around online advertising disclosures.

Despite his high-profile position running one of the world’s largest companies, Zuckerberg typically prefers to speak through Facebook posts and events rather than interviews.

After his post on Wednesday, Zuckerberg was criticized by some on social media for stopping short of an outright apology.

“This was a major breach of trust, and I’m really sorry that this happened,” Zuckerberg said. “We have a basic responsibility to protect peoples’ data.”

Zuckerberg expressed regret for not doing more to take action against Cambridge Analytica when the issue came to the company’s attention in 2015. At the time, Facebook demanded and received a formal certification from the firm that it had deleted all user data acquired through improper means.

“I don’t know about you, but I’m used to when people legally certify that they are going to do something, that they do it. But I think this was clearly a mistake in retrospect,” Zuckerberg said. “We need to make sure we don’t make that mistake ever again.”

This week has brought another black eye for the company after what was already a bruising year full of stories about fake news, foreign election meddling, filter bubbles and social media addiction.

When asked if bad actors are currently trying to use Facebook to meddle in the U.S. midterm elections, Zuckerberg said, “I’m sure someone’s trying.” But he expressed confidence in his company’s ability to tackle it.

“This isn’t rocket science. There’s a lot of hard work we have to do to make it harder for nation states like Russia to do election interference,” he said. “But we can get in front of this.”