Updated at 3:08 p.m. ET
After five hours of testimony before a joint session of two Senate committees on Tuesday, Facebook CEO Mark Zuckerberg returned to the Capitol for a second straight day of grilling — this time before the House.
For another five hours, Zuckerberg took questions from the House Energy and Commerce Committee. Representatives took a generally sharp tone, pushing Zuckerberg to commit to yes or no answers and occasionally exclaiming with mock surprise when he protested that he couldn't answer.
And the questions extended far beyond security, privacy and data sharing, to address diversity at Facebook headquarters and whether the company is tacitly allowing illegal drug sales on the platform.
You can watch video of the proceedings above, or on YouTube via PBS. Or, of course, read on for highlights.
The congressional hearings, Zuckerberg's first, come in the wake of a scandal in which Facebook user data was sold to Cambridge Analytica, a third-party group that assisted the Trump campaign. (Cambridge Analytica says it did not use the Facebook data in its 2016 election work.)
Zuckerberg has repeatedly apologized for the Cambridge Analytica scandal, while blaming the information sharing on a researcher who, according to Facebook, violated the platform's terms of service.
Zuckerberg says he found out that the data were sold to Cambridge Analytica after The Guardian reported on the issue.
"Do you routinely learn about these violations through the press?" Rep. Mike Doyle, D-Pa., asked on Wednesday.
"Sometimes we do," Zuckerberg said.
He told members of the House that his own data were included in the privacy breach.
A few of the other topics discussed in the hearing:
What is Facebook?
Rep. Greg Walden, R-Ore., committee chairman, noted that Facebook has exclusive broadcasting deals as well as tools that allow people to transfer money.
"Is Facebook a media company?" he asked. "Is Facebook a financial institution?"
Zuckerberg replied: "I consider us to be a technology company because the primary thing that we do is have engineers that write code and build products and services for other people. There are certainly other things that we do. ... We build planes to help connect people, and I don't consider us to be an aerospace company."
Facebook has been testing planes that broadcast internet signals to the ground.
Does Facebook's data collection amount to surveillance of users?
Rep. Bobby Rush, D-Ill., accused Facebook of "the wholesale invasion and manipulation of users' right to privacy."
"What is the difference between Facebook's methodology and the methodology of the American political pariah J. Edgar Hoover?" he asked.
"The difference is extremely clear, which is that on Facebook you have control over your information," Zuckerberg said. "The content that you share, you put there. ... The information that we collect, you can choose to have us not collect. You can delete any of it, and of course, you can leave Facebook if you want.
"I know of no surveillance organization that gives people the option to delete the data that they have or even know what they're collecting," Zuckerberg said.
Do consumers understand what they've agreed to as they use Facebook?
Walden asked Zuckerberg, "Did it ever cross your mind that you should be communicating more clearly with users about how Facebook is monetizing their data?"
"I would say that we do try to explain what we do as time goes on," Zuckerberg said. Every time someone adds content to Facebook, he said, there is "a control right there about who you want to share it with. ... I think that in the product that's quite clear. I do think that we can do a better job of explaining how our advertising works."
Rep. Michael Burgess, R-Texas, approached the same question from a different angle. "Can the average layperson look at the terms and conditions and make the evaluation: Is this strong enough protection for me to enter into this arrangement?" he asked.
Zuckerberg said, "I think if someone wanted to know that they could, but a lot of people probably just accept terms of service without taking the time to read through it. I view our responsibility not as just legally complying with laying it out, getting that consent, but actually trying to make sure that people understand what's happening throughout the product."
He repeatedly said he believes users do understand how their data will be used. Multiple lawmakers expressed skepticism on that point.
The question of financial penalties
In an occasionally tense exchange, Rep. Diana DeGette, D-Colo., challenged Zuckerberg over his company's billions of dollars in profit and what she described as the lack of financial penalty over prior privacy breaches.
She cited two settled class-action lawsuits — Lane v. Facebook, in which users received no compensation, and Fraley v. Facebook, in which users received $15 each. DeGette expressed surprise when Zuckerberg said he was not familiar with the details of the cases.
She also asked whether there was a financial penalty involved after a Federal Trade Commission investigation ended in a 2011 consent decree. Zuckerberg said he couldn't remember, which prompted more skepticism from DeGette.
"The reason you probably don't remember is because the FTC doesn't have the authority to issue penalties for first-time violations," she said.
"We continue to have these abuses and these data breaches, but at the same time, it doesn't seem like future activities are prevented," DeGette said. "I think one of the things that we need to look at in the future ... is putting really robust penalties in place in case of improper actions."
On racial diversity within Facebook's staff and leadership
Congressional Black Caucus member Rep. G.K. Butterfield, D-N.C., said that Facebook lists five leaders on its website, none of whom are black. "This does not reflect America," he said.
"We have a broader leadership than just five people," Zuckerberg said.
"Do you plan to add an African-American to your leadership team in the foreseeable future and will you commit that you will continue to work with us, the Congressional Black Caucus, to increase diversity within your company?
"Congressman, we will certainly work with you," Zuckerberg said. "This is an important issue."
Butterfield asked for data on the retention of employees by race; Zuckerberg said he would discuss it with his team.
Rep. Yvette Clarke, D-N.Y., also pushed Zuckerberg hard on the question of diversity, tying the "monolithic" makeup of the company to Facebook's failures to anticipate and prevent disinformation campaigns.
Is Facebook doing enough to stop opioid sales?
Rep. David McKinley, R-W.Va., brought up America's opioid crisis and posted a photo of drugs available for sale on Facebook, no prescription necessary.
"Your platform is still being used to circumvent the law and allow people to buy highly addictive drugs without a prescription," he said. "Facebook is actually enabling an illegal activity and in so doing, you are hurting people."
Zuckerberg replied that "there are a number of areas of content that we need to do a better job policing on our service."
"You've said before you were going to take down those ads but you didn't do it," McKinley said. "When are you going to take them down? ... Where is your accountability to allow this to be occurring?"
Zuckerberg said Facebook relies on users flagging inappropriate content to be taken down. He said with billions of pieces of content shared daily, it was not feasible for the company to examine all those posts. But he said the company hopes to use artificial intelligence tools to help flag inappropriate content.
On Facebook's collection of data on non-Facebook users
Zuckerberg's congressional testimony has focused on how Facebook handles user data. But Rep. Ben Luján, D-N.M., pushed Zuckerberg on how exactly Facebook uses the data of people who are not users of the service.
Their conversation went like this:
Luján: "Facebook has detailed profiles on people who have never signed up for Facebook, yes or no?"
Zuckerberg: "In general, we collect data from people who have not signed up from Facebook for security purposes."
Luján: "... On average, how many data points does Facebook have on each Facebook user?"
Zuckerberg: "I do not know off the top of my head."
Luján: "The average for non-Facebook platforms is 1,500. It's been reported that Facebook has as many as 29,000 data points for an average Facebook user. Do you know how many points of data Facebook has on the average non-Facebook user?"
Zuckerberg: "Congressman, I do not off the top off my head, but I can have our team get back to you afterwards."
Luján: "I'd appreciate that. It's been admitted by Facebook that you do collect data points on non-Facebook users, so my question is, can someone who does not have a Facebook account opt out of Facebook's involuntary data collection?"
Zuckerberg: "Congressman, anyone can turn off and opt out of any data collection for ads, whether they use our services or not, but in order to prevent people from scraping public information ... we need to know when someone is trying to repeatedly access our services ... "
Luján: "You've said everyone controls their data but you are collecting data on people who are not even Facebook users, that have never signed a consent, a privacy agreement, and you're collecting their data. And it may surprise you that on Facebook's page, when you go to 'I don't have a Facebook account and would like to request all my personal data stored by Facebook,' it takes you to a form that says, 'Go to your Facebook page and then on your account settings you can download your data.' ... You're directing people who don't even have a Facebook page to have to sign up for a page to reach their data. We've got to fix that."
How does Facebook use information it collects, as opposed to what users provide?
In his testimony, Zuckerberg has consistently emphasized the information people voluntarily supply to Facebook — photos they upload, status updates they write, pages they click "like" on. He says people own that data and can delete it at any time. He also stresses that Facebook, while it uses that data to power its ad business, does not sell the data itself to advertisers.
Rep. Joe Kennedy, D-Mass., pressed Zuckerberg on something different — the "metadata" about users that Facebook gathers without users uploading it themselves. That includes things like when and how users access Facebook, and what they click on or look at, including on sites other than Facebook. (The Wall Street Journal recently published a visual breakdown of data provided vs. data collected by various platforms.)
"There's an awful lot of information that is generated that people don't think that they're generating, and that advertisers are being able to target because Facebook collects it," Kennedy said.
"Yes," Zuckerberg said. "My understanding is that the targeting options that are available for advertisers are generally things that are based on what people share. Now, once an advertiser chooses how they want to target something, Facebook also does its own work to rank and determine which ads are going to be interesting to which people. So we may use metadata or other behaviors of what you've shown that you're interested in in news feeds or other places in order to make our systems more relevant to you, but that's a little bit different from giving that as an option to an advertiser."
"I don't understand how users then own that data," Kennedy said. He then ran out of time for questions.
On its business help pages, Facebook tells advertisers it can target ads based on, among other things, users' purchase behaviors and "activities people engage in on and off Facebook."
Members of Congress also asked pointed questions about how Facebook will defend civil rights — by preventing housing discrimination in advertising, for instance — whether the platform suppresses conservative speech or might in the future, and the degree of responsibility Facebook has over content on its platform, including disinformation.
On Tuesday, the hearing before the Senate covered many of the same topics as well.
As NPR's Peter Overby reported earlier this week, Facebook — like Silicon Valley in general — has grown more involved in Washington politics over the years:
"Facebook opened its D.C. office when it was five years old — and already worth billions. It routinely hires lots of top-tier, veteran lobbyists, as does Google.
"The current lobbying environment is ideal. Many lawmakers still don't fully grasp the technology. Congress long ago defunded its in-house technology office, which could have taught them.
"Facebook reported its 2017 lobbying cost at nearly $12 million. Google spent even more: $18 million. ... Some of the money goes to think tanks, where experts can shape policy debates on Capitol Hill. ... Then there's campaign money. ...
"Facebook's PAC and employees made political contributions totaling $4.5 million in the 2016 cycle, according to the nonpartisan Center for Responsive Politics. For Google's parent company, Alphabet, the total was nearly $8 million."