Embattled Facebook CEO Mark Zuckerberg will draw the anger and frustration of both Republican and Democratic lawmakers Tuesday, when he sits for a joint Senate hearing to field questions about data security, his effort to police "fake news" that appears on his giant media site, and foreign government meddling in the 2016 presidential election.

Zuckerberg seemed to acknowledge the seriousness of the questions facing his company by donning a suit as he made an initial round of meetings Monday, a far cry from the casual T-shirt he often wears.

At the top the list of questions he will field will most certainly be the improper exposure of the information of more than 87 million Facebook users to data firm Cambridge Analytica, which worked on the Trump campaign ahead of the 2016 election. Facebook had originally said 50 million users were affected, but increased that estimate substantially last week.

Cambridge Analytica has blamed a contractor for its unauthorized access to most of those accounts, but the blame this week will fall on Zuckerberg and the failure of his company to see what was happening.

“If Facebook can’t fix its privacy problems, then how can Americans trust them to be caretakers of their sensitive information?” said Sen. Bill Nelson, D-Fla., in a statement after meeting with Zuckerberg privately on Monday.

Facebook admitted last week that data from most of its 2 billion users could be at risk due to a feature that allowed people to enter another person’s phone number or email address in order to search for them.

“However, malicious actors have also abused these features to scrape public profile information by submitting phone numbers or email addresses they already have through search and account recovery,” Facebook said in a blog post. “Given the scale and sophistication of the activity we’ve seen, we believe most people on Facebook could have had their public profile scraped in this way.”

Just who are those “malicious actors,” and what data do they actually have? Lawmakers will want to know.

“How can Facebook be sure more user data has not been misused, and how can the company identify other third parties that may have inappropriately acquired or misused user data?” Michelle De Mooy, director of the Privacy & Data Project at the Center for Democracy & Technology, wrote in a recent blog post.

De Mooy added: "Are legal remedies sufficient to enforce Facebook’s data sharing policies? If not, has the company put in place any technical measures to ensure that third parties with access to Facebook data use it appropriately?"

He'll also face the issue of Russia's election meddling and is expected to say that Facebook was “too slow” to notice and then stop the ways Russia used the global media platform to influence the 2016 U.S. presidential contest.

The recent roll-out of new data-sharing policies and how users can control their privacy and security settings may not be enough to satisfy lawmakers, who have long been critical of how Facebook will change that heading into the next round of elections — both at home and abroad.

In his prepared remarks for a follow-up hearing on Wednesday in the House, Zuckerberg took responsibility and apologized.

"We didn't take a broad enough view of our responsibility, and that was a big mistake," Zuckerberg said. "It was my mistake, and I'm sorry. I started Facebook, I run it, and I'm responsible for what happens here.”

Zuckerberg will likely have to apologize many more times today before the House on Wednesday and will be questioned if he remains the right person to run the company.

The social media platform was founded and launched by Zuckerberg in 2004, and as of January, it has more than 2.2 billion monthly active users. Facebook has made Zuckerberg a rich man: His net worth is an estimated $62.2 billion.

This week's hearings and possible policy responses from Congress threaten to upend his wildly successful platform. Already, some users are walking away from Facebook, worried about the safety of the information stored therein.

“Users should have better options when they decide where to spend their time and attention online,” wrote Gennie Gebhart of the Electronic Frontier Foundation. “Facebook and other companies must respect user privacy by default and by design. If you want to use a platform or service that you enjoy and that adds value to your life, you shouldn't have to leave your privacy rights at the door.”