US Lawmakers Demand Changes of Facebook's CEOU.S. lawmakers on Tuesday demanded better personal data protection at Facebook, whose CEO, Mark Zuckerberg, weathered heated questions from two Senate panels over data breaches affecting tens of millions of users of the mammoth social media platform. "There was clearly a breach of consumer trust and a likely improper transfer of data," said Judiciary Committee Chairman Chuck Grassley, an Iowa Republican. "If you and other social media companies do not get your act in order, none of us are going to have any privacy," the top Democrat on the Commerce Committee, Bill Nelson of Florida, said. "If Facebook and other online companies will not or cannot stop the privacy invasions, then we are going to have to — we, the Congress." Zuckerberg was called to testify after news emerged that the personal data of millions of Facebook users had been harvested without their knowledge by Cambridge Analytica, a British voter-profiling company that President Donald Trump's campaign hired to target likely supporters in 2016. WATCH: Zuckerberg Takes Responsibility for Inadequately Protecting User Data No media source currently available Zuckerberg repeatedly has apologized and promised to make amends, and did so again on Capitol Hill. The social media mogul spoke with pride about Facebook's ability to connect people for the common good, but he admitted the company had not been proactive in safeguarding its users from misuse of data or those sowing malign messages. "It was my mistake, and I'm sorry," Zuckerberg said. "I started Facebook, I run it. And I'm responsible for what happens here." Earlier this week, Facebook began notifying 87 million users, most of them in the United States, whose personal data might have been mined by Cambridge Analytica.\n\nZuckerberg pledged that Facebook would scrutinize and, when necessary, block other firms from gaining access to the platform and empower its 2.2 billion users to wall off their apps from third parties. Zuckerberg is to testify Wednesday before a House panel. Lawmakers pledged to hold separate hearings focusing on Cambridge Analytica soon.