Facebook on Thursday took down a Trump campaign ad that used an inverted red triangle — a Nazi symbol used to designate political prisoners in concentration camps — to target “far-left” groups and so-called antifa.

The ads appeared in paid posts by the Team Trump campaign as well as by President Donald Trump and Vice President Mike Pence. They began running on Wednesday and had as many as 1 million impressions before being taken down, The Washington Post reported.

“We removed these posts and ads for violating our policy against organized hate,” a Facebook spokeswoman said in an email. “Our policy prohibits using a banned hate group’s symbol to identify political prisoners without the context that condemns or discusses the symbol.”

The Facebook ads said, “Dangerous MOBS of far-left groups are running through our streets and causing absolute mayhem. They are DESTROYING our cities and rioting — it’s absolute madness.” Below the copy was the inverted red triangle that Nazis used to designate political prisoners.

Facebook’s action became public as the House Intelligence Committee was holding a virtual hearing on how social media platforms including Facebook, Twitter and Google handle disinformation from a variety of fronts.

All Republican members of the committee refused to participate in the hearing, Rep. Adam B. Schiff, D-Calif., the chairman of the panel said. This is the second time that the panel’s minority, led by Rep. Devin Nunes, R-Calif., a close ally of Trump’s, has been completely absent from a hearing.

Rep. Eric Swalwell, D-Calif., a member of the committee, said this was the third instance of Facebook removing an offending Trump campaign ad. Swalwell also asked if Facebook would block the Trump campaign account for repeated violations of using hateful symbols.

Nathaniel Gleicher, Facebook’s head of cybersecurity operations, said, “if we see repeated instances of violations or misinformation, for example, we’ll take increasing actions.”

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Facebook is under mounting pressure both from within its own ranks and from outside observers and lawmakers on how it handles Trump’s inflammatory posts and other manipulated content.

Unlike Twitter, which has said it would not allow political advertising, Facebook continues to accept political ads. The platform also recently allowed Trump’s post that said, “when the looting starts the shooting starts,” a phrase from the 1960s that referred to a violent response to civil-rights protests. Twitter, in contrast, placed a warning label on a similar post on its platform.

During the Intelligence Committee hearing, Gleicher, when pressed to explain the company’s decision, said, “I personally found the post to be abhorrent,” but that he was not involved in the decision to allow Trump’s post to remain on the platform.

All social media companies are also under pressure as the Trump administration and several Republican lawmakers are calling for diluting protections the companies enjoy under U.S. law, which frees them from liability for content on their platforms.

Executives from Facebook, Twitter and Google told the committee that they were routinely working with the FBI and other government agencies to share and track information on foreign influence operations on their platforms and taking down misinformation related to the November presidential and congressional elections.

Despite several investigations that unearthed the role of Kremlin-backed hackers in influencing American voters in the 2016 elections and stepped up vigilance by the social media platforms as well as careful monitoring by several security experts, Schiff said he remained concerned about foreign influence in the election.

“As I look across the landscape, I can’t say that I’m confident that the 2020 election will be free of interference by malicious actors, foreign or domestic, who aspire to weaponize your platforms to divide Americans against one another and weaken our democracy,” Schiff said.

Swalwell asked Facebook, Twitter and Google how they planned to address a possible scenario where Trump loses the election and between Election Day and the January inauguration of a new president, Trump encourages foreign influence operations aimed at discrediting results of the election, and amplifies misinformation.

Executives of all three companies said they would apply their existing rules uniformly and consistently to remove any misinformation from their platforms.

Facebook’s Gleicher said the company was conducting so-called red-team exercises — similar to what the U.S. military does to prepare for possible enemy actions — to understand how to respond to various post-election scenarios.

“The period after election is a crucial one, given that we expect an increase in vote by mail,” Gleicher said. It may take a little longer than usual to count a large volume of mailed ballots and Facebook is aware that the additional time could be used to sow doubts about the outcome, he said.