The second round of congressional hearings for Mark Zuckerberg is happening now, as he testifies before the House Energy and Commerce Committee. Facebook's co-founder and CEO was questioned for over five hours on Tuesday by the Senate Commerce and Judiciary Committees, with senators urging him to avoid a "nightmare" for users on his site. That, of course, after Facebook failed to protect personal data of up to 87 million users from being misused by political research firm Cambridge Analytica. Zuckerberg's opening statement today echoed what he said during the first hearing: "It was my mistake, and I'm sorry. I started this company and I'm responsible for what happens here."