The lawmakers questioning Facebook CEO Mark Zuckerberg are not strangers to politics on Facebook — many have paid to use its microtargeted advertising technology in campaigns.

In all, 43 lawmakers sit on the Senate Judiciary and Commerce committees, along with 55 on the House Energy and Commerce panel. And every one of them has a verified Facebook page.

Zuckerberg’s appearance on the Hill comes after revelations that a British firm obtained Facebook user data under questionable circumstances. Cambridge Analytica reportedly used the data to create hyper-targeted political advertisements for President Donald Trump’s campaign.

Both Sen. Ted Cruz, who serves on the two Senate committees set to grill the Facebook founder Tuesday, and Sen. Thom Tillis, who’s on the Judiciary committee, used Cambridge Analytica for political campaigns in the past.

What brought Zuckerberg to the Hill — and the widespread use of Facebook by lawmakers — illustrates the murky relationship between politics, social media and big data.

Legislating that relationship may be complicated. Regulating data collection and advertising could make it harder for politicians to campaign online and limit their Facebook presences. Regulation could also undermine Facebook’s business model, making it less attractive to advertisers.

Many campaigns use data collection apps similar to Cambridge Analytica’s. In 2016, mobile apps for the primary campaigns of Cruz, Sen. Bernie Sanders, Gov. John Kasich and Ben Carson gathered Facebook data from their downloaders that sometimes included location and phone contacts.

Unlike Cambridge Analytica, those apps explicitly stated the information would be shared with the candidate’s political campaign. However, the apps still automatically shared data from the user’s Facebook friends, who did not give permission.

Zuckerberg is expected to face questions about what happens to personal information on Facebook and other privacy issues.

Watch: Three Democrats Who Own Facebook Shares Will Question Zuckerberg

The Energy and Commerce committee hearing is “about first gathering the facts and shedding light on how Facebook’s business model impacts consumers,” Elena Hernandez, the committee’s press secretary, said in an email.

“Members will have the opportunity to ask directly how Facebook uses and protects the personal information of its 2 billion users,” Hernandez said.

The Federal Trade Commission is also investigating whether Facebook violated a 2012 privacy consent order, Hernandez said.

Limited oversight

Experts say there’s been little focus on how Facebook’s data collection and targeted ad practices allowed for data leaks.

“Facebook keeps talking about how they will protect against ‘bad actors’ like hackers, malicious third parties and people misusing their platform, but never talks about how Facebook will protect you from Facebook,” said Gennie Gebhart, a researcher at the Electronic Frontier Foundation, a privacy nonprofit. “Facebook is the one’s collecting data that can stolen from those third party actors in the first place, and any protections on the third party end are just Band-Aids.”

Cambridge Analytica obtained the private information of up to 78 million Facebook users by creating a personality quiz app that gave users results only if they granted the firm permission to access their Facebook data. Users who gave permission were told their information would be used for “academic purposes only.”

That information was used by campaigns working with Cambridge Analytica to target individual Facebook users during the 2016 election, said Angelo Carusone, president of Media Matters, a not-for-profit media watchdog.

Big data tools help advertisers and politicians target their messages based on demographics and interests.

Facebook’s advertising tools identify groups of people by demographics and interests, but not specific individuals. Advertising to a group, rather than targeting individuals, may be less effective and more costly.

“The difference is with Cambridge’s data, I can run the ad directly to you and it costs 1 cent,” Carusone said.

Facebook recently clarified what data is kept and shared in its terms of service.

But that may not reach many social media users. A 2016 University of Connecticut study found that only one in 500 participants read terms of service online before clicking “agree.”

Facebook has no intention of changing how much data it collects or the way it sells that data to advertisers, Zuckerberg said in a Q&A the company posted online last week.

“The way to make the ads good is by making it so that when someone tells us they have an interest, they like technology or they like skiing or whatever it is they like, that the ads are actually tailored to what they care about,” Zuckerberg said.

The company’s success relies heavily on its ability to create and sell hyper-targeted advertising niches.

“No one wants their personal information sent to campaign consultants without their permission, regardless of who they vote for,” Sen. Amy Klobuchar, a Minnesota Democrat, said on Facebook last week. “As we move forward, the Congressional hearings are critical; we need more privacy protections in law.”

A political tool

Political candidates can take advantage of this data-led marketing the same way businesses can, and Facebook often helps campaigns strategize.

Brad Parscale, the Trump campaign’s digital director, recently told “60 Minutes” that Facebook sent staff to help the Trump campaign target its advertising. Facebook advised Trump’s campaign on how to create microtargeted ads, many that were meant to reach only one individual, Parscale said.

“I asked each [Facebook employee] by email, ‘I want to know every single secret button, click, technology you have,’” Parscale said during the interview. “And I want your people here to teach me how to use it.”

Parscale said Facebook also offered to help the Clinton campaign but was turned down.

In a statement provided to “60 Minutes,” Facebook said it offers support to political campaigns regardless of party.

Watch: Three Democrats Who Own Facebook Shares Will Question Zuckerberg

Facebook also came under fire earlier this year when the Senate Intelligence committee investigated advertisements and content produced by the Internet Research Agency, a group based in Saint Petersburg with ties to the Russian government. In September, Facebook turned over to Congress more than 3,000 advertisements on its site from 470 fake accounts and pages run by the Russian organization.

The Internet Research Agency’s advertisements reached over 146 million Americans during the 2016 election.

Carusone said Cambridge Analytica likely had less of an effect on the election than the Internet Research Agency. But the British firm’s data tools may still be available.

Third parties, including campaigns that used the firm, may still have copies of the Cambridge Analytica data sets, which could create an unfair advantage, he said.

“Facebook punishes the people who take the data, but what if there are two or three copies that are still out there?” Carusone said.

Using and collecting data for targeted political campaigns is not new. Cambridge Analytica itself has been in operation since 2013, and one of its first targeted voter advertisement campaigns was for Tillis’ campaign.

The firm highlights the North Carolina Republican’s successful bid to unseat former Sen. Kay Hagan in the 2014 midterm elections as an example of how it uses data to create and disperse targeted marketing. The News & Observer reported Tillis’ campaign paid the firm $30,000 during the election cycle.

The North Carolina Republican Party also paid Cambridge Analytica $150,000 and the John Bolton Super PAC, which was involved in the Tillis race, paid $341,000 in 2014.

Tillis did not respond to requests for comment.

By 2016, Cambridge Analytics was used by multiple campaigns during the 2016 election. Cruz’s primary campaign paid Cambridge Analytica more than $5.8 million, according to Federal Election Commissions records.

“The campaign hired Cambridge Analytica as a vendor to assist with data analysis and online advertising,” Catherine Frazier, a spokeswoman for the Texas Republican, said in a statement released in March. “The campaign’s data analysis program followed and built upon the successful data-modeling and micro-targeting approach pioneered by the Obama campaigns in 2008 and 2012.”

Frazier said the firm guaranteed Cruz’s campaign that it attained all its data legally.

After Cruz stopped using Cambridge Analytica during the Republican primaries, the firm went on to work for President Donald Trump’s campaign.