The hearing is expected to highlight the partisan divisions over Silicon Valley’s recent crackdown on misinformation. Republicans leading the hearing have accused the companies of going too far in labeling or otherwise limiting the spread of falsehoods on their platforms, saying it amounts to censorship of their views. Democrats have said the companies have not done enough, especially as Trump and his allies continue to use Twitter and Facebook to spread claims of election fraud without evidence.

Senate Judiciary Committee Chairman Lindsey O. Graham (R-S.C.) kicked off the hearing by calling for changes to Section 230, a law that protects Internet companies from much liability for what their users post online. That law was the focus of the hearing with tech executives three weeks ago. Graham hardly mentioned the companies’ actions during the election and the days following.

“When you have companies that have the power of governments, have far more power than traditional media outlets, something has to give,” Graham said. Graham and Sen. Richard Blumenthal (D-Conn.) have introduced bipartisan legislation to reform Section 230, called the EARN IT Act.

The chief executives are expected to be on the defensive, again. Dorsey is expected to push back on long-running accusations based on specious evidence that the company is biased against conservatives, according to a preview of his testimony.

Dorsey plans to reiterate the company’s commitment to fact checking in his prepared testimony Tuesday, pointing out that Twitter labeled about 300,000 tweets in the lead-up to the election and the week following on content that was potentially misleading.

“We want to be very clear that we do not see our job in this space as done,” Dorsey will say. “Our work here continues, and our teams are learning and improving how we address these challenges and earn the trust of the people who use Twitter.”

Facebook’s Zuckerberg plans to focus on the company’s efforts to combat misinformation and voter suppression. Zuckerberg will say the company removed false claims about polling conditions in coordination with local law enforcement and displayed warnings on more than 150 million pieces of content reviewed by third-party fact-checkers. He will also explain the company’s election labels, which appended information about the election results and voting to posts from both Trump and Joe Biden.

“We’re committed to doing everything we can to protect our community while supporting free expression and democracy, but as I’ve said before, we don’t think that tech companies should be making so many decisions about these important issues alone,” Zuckerberg will say.

Tech chief executives have become a common fixture on Capitol Hill as the political backlash against social media companies has swelled in recent years. Zuckerberg avoided testifying in front of Congress at all for the first 14 years of Facebook’s existence, but this will be his third virtual appearance just since July.

Dorsey has been a far less frequent witness, but it’s likely he may see even more ire from Republicans at this hearing. The company has taken some more-extreme steps in recent weeks to shield posts from Trump that make false or unsubstantiated claims about the election.

Twitter said its labeling accounted for about 0.2 percent of all election-related content. But researchers have said there is still not enough data available to determine how effective the interventions were.

Tuesday’s hearing was scheduled last month after Republicans on the committee voted to subpoena the chief executives of Twitter and Facebook in response to unusual steps they took to limit the spread of New York Post articles on their platforms. The articles centered on emails allegedly sent by Biden’s son Hunter Biden. The Washington Post has not substantiated the emails.

The chief executives ultimately agreed to appear in front of the panel voluntarily. Graham said in a statement that the hearing would focus on the “censorship and suppression” of the articles and that it would also provide lawmakers “a valuable opportunity to review the companies’ handling of the 2020 election.”

Dorsey and Zuckerberg defended their handling of the New York Post articles at last month’s hearing. Yet they are not out of the woods on the issue. Twitter has changed its policies in response to the backlash, and Dorsey has apologized for taking the extreme step of blocking URLs to the articles.

Sen. Marsha Blackburn (R-Tenn.), who leads the committee’s tech task force, plans to question the executives about a recent conversation she had with an op-ed editor of the New York Post about the tech companies’ decisions to limit the articles’ spread.

Democrats, meanwhile, plan to focus on Trump’s use of social media to spread baseless claims about mail-in ballots and voting machines. Blumenthal accused the companies of giving the president a megaphone to spread falsehoods “in an apparent attempt to overturn the will of the voters.” He said the companies’ efforts are only “baby steps” and called on them to take greater responsibility for their services.

Blumenthal noted that no executive from Google, which owns YouTube, was called to testify at today’s hearing. He criticized Google for being less aggressive about misinformation than Facebook and Twitter. He also said he hopes that the committee could have a series of hearings on tech issues in the future, addressing issues including antitrust and Section 230.

Blumenthal also called the Republicans’ focus on censorship a “political sideshow.”

“This hearing is a betrayal of the real victims of the real harms caused by Big Tech,” he told Dorsey and Zuckerberg. “You have repeatedly and catastrophically failed the American public.”

The hearing could provide a key preview of Democrats’ top concerns with social media companies as they prepare to regain control of the White House. The Biden campaign has had a publicly contentious relationship with Facebook and repeatedly accused the company of not going far enough to prevent the spread of election-related misinformation. Democrats are also pushing for more-aggressive antitrust enforcement against the tech industry, and the Federal Trade Commission is expected to file an antitrust lawsuit against Facebook as early as this month.

The repeated hearings have given lawmakers a platform to air their grievances with Silicon Valley, but so far little meaningful regulation has resulted from them.

Zuckerberg and Dorsey’s last appearance was purportedly focused on overhauling a law that shields Internet companies from much legal liability for what their users post, but it turned into a back-and-forth about labeling and censorship claims.

“We have taken action on tweets from leaders all around the world, including the president,” Dorsey said in response to Republican questioning about fact-check labels.