Facebook’s chief executive, Mark Zuckerberg, will make his much-anticipated appearance before members of Congress starting Tuesday afternoon. In two days of hearings, he will face tough questions on how and why the company failed to protect the delicate data of many millions of its users.

The hearings were prompted by the revelation that Cambridge Analytica, a British political consulting firm linked to the Trump campaign, harvested data of an estimated 87 million Facebook users to psychologically profile voters.

But expect the hearings to expand far beyond the Cambridge matter. Senate and House lawmakers will take the opportunity to grill Mr. Zuckerberg, the 33-year-old iconic Silicon Valley entrepreneur, on the proliferation of so-called fake news on Facebook and on Russian interference on the platform during the 2016 presidential election.

Regulation and legal action could loom for the company. The joint Senate Judiciary and Commerce Committees will hold their hearing at 2:15 p.m. Tuesday. Mr. Zuckerberg will appear before the House Energy and Commerce Committee at 10 a.m. Wednesday.

Here are five things to watch as Mr. Zuckerberg finally takes the hot seat.

In Zuckerberg We Trust?

Facebook’s repeated privacy mishaps — and subsequent apologies — will be a recurring theme during the hearings.

Mr. Zuckerberg will start out with another mea culpa and plans to tell lawmakers that the company made a “big mistake” in underestimating its responsibility, according to prepared testimony released by the Energy and Commerce Committee. “It was my mistake, and I’m sorry. I started Facebook, I run it and I’m responsible for what happens here.”

Mr. Zuckerberg is also expected to say the company is hiring thousands of people to make the site more secure and to correct mishaps over privacy and fake news. But the question of trust is at the center of the company’s ability to thrive going forward. Some lawmakers will insist that the company’s business model of collecting data to target ads is fundamentally at odds with the protection of its users’ privacy.

Privacy Regulation

Democrats and some Republicans will raise the need for privacy regulations, saying tech companies cannot be counted on to do it voluntarily. They will point to data protection laws that are about take effect in Europe as a guide.

Mr. Zuckerberg is expected to say that he supports those European laws and that the same tools for privacy will be available to all of Facebook’s two billion users. But the details will matter, and some lawmakers will insist that those settings and tools are made clearly available to users and are the default setting.

Eye on Republicans

Democrats will be among the most vocal critics of Facebook, but it is worth watching what regulation-wary Republicans convey during the hearings. If Republican lawmakers indicate that they believe privacy laws are needed or that the Federal Trade Commission needs to clamp down harder on its enforcement of companies like Facebook, that could portend real change.

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Their comments could guide the incoming members of the commission, who are inheriting the agency’s investigation of Facebook’s violations of its 2011 agreement on privacy protections.

Is Facebook a Media Company?

A central question surrounding Facebook is whether it is a media company. It is the world’s largest platform for news and information and has thousands of people now making decisions on editorial content.

Lawmakers — like Senator Ted Cruz, Republican of Texas — are expected to focus on whether the company’s algorithms and staff suppress conservative views or if they skew content with a political bent.

The determination as to whether Facebook is a media company is critical: If it’s defined as a media company, Facebook could face many more regulatory pressures, including at the Federal Communications Commission.

Leadership

In Mr. Zuckerberg’s first appearance before Congress, the world will consider his performance as a statesman and as a business executive.

To help make the case that he should be taken seriously, Mr. Zuckerberg will be taking oath in a suit instead of his trademark gray T-shirt and jeans.

Some lawmakers may ask if he is capable of leading such an important company, one that some in Washington view as a sort of utility for information. He will need to come across as more than a brilliant engineer and as someone who understands the influence Facebook wields and its responsibility.

Wall Street, employees and global regulators will see the company and its brand through the lens of Mr. Zuckerberg’s marathon testimonies.