It was about three hours into Facebook CEO Mark Zuckerberg’s testimony to the House Energy and Commerce Committee on Wednesday, when all of the attention quickly shifted from Zuckerberg’s glistening brow to the exhibit looming over Missouri Republican Billy Long's head.

"Who are they?" Long asked, referring to the two women whose larger-than-life faces filled the giant poster board.

Zuckerberg paused, before offering, almost in question, "I believe…is that Diamond and Silk?"

Of course, Zuckerberg by then knew them well. It wasn't the first time members of Congress had asked him about the two Trump-supporting internet celebrities that day, and it wouldn't be the last. Again and again, Republican members of the committee asked the embattled founder why Diamond and Silk recently received a message explaining that their Facebook Page’s reach was being throttled because their content was considered “unsafe to the community.”

“What is unsafe about two black women supporting President Donald J. Trump?” Long asked accusingly.

It became clear that Zuckerberg was being grilled as much for the perceived suppression of conservative thought as he was for lax data policies.

If Zuckerberg sounded befuddled in response, perhaps it was because he expected to discuss Facebook's recent data privacy scandal on Capitol Hill, not the particulars of any one Facebook Page. Diamond and Silk's names don’t appear to be in the notes Zuckerberg used to prepare for his face time with Congress—the same goes for their real names, Lynnette Hardaway and Rochelle Richardson, respectively. Neither does another word: censorship. And yet, over the course of the five-hour hearing Wednesday, it became clear that Zuckerberg was being grilled as much for the perceived suppression of conservative thought as he was for lax data policies. In a way, Zuckerberg was testifying before two simultaneous, but distinct, hearings: one helmed by privacy advocates on the left, and another by free-speech defenders on the right.

From the start, Wednesday's interrogation of Zuckerberg proved more partisan than the joint hearing of the Senate he attended the day before. Ranking member Frank Pallone, Jr. skewered Republicans in his opening remarks for continuing to "block or even repeal the few privacy protections we have." Meanwhile, Republican representatives accused liberal lawmakers of hypocrisy for expressing so much outrage about Cambridge Analytica. "They were high-fiving what took place in 2012 with President Obama," said Michigan's Tim Walberg, referring to the Obama campaign's own use of Facebook data in political advertising.

With these divisions laid bare, lawmakers' questions mainly came down along party lines. Democrats hit Zuckerberg with a fresh round of questions about Facebook's fundamentals, echoing their counterparts in the Senate on Tuesday. Their limited patience flustered Zuckerberg, as he struggled to provide short answers about whether Facebook collects browsing data on its users (it does) or collects data about people who don't have Facebook profiles (it does that, too). Pallone, in particular, pressed Zuckerberg to say whether Facebook is prepared to change its default user settings to minimize "to the greatest extent possible" the collection of user data. "Congressman, this is a complex issue that I think deserves more than a one-word answer," Zuckerberg replied, to Pallone's disappointment. Zuckerberg said he'd follow up.

When it was their turn at the microphone, Republican lawmakers took a markedly different approach, zeroing in on what they see as pervasive censorship of conservatives at Facebook. It didn't arise out of thin air. Facebook first began facing these questions in early 2016, when members of Facebook's Trending Topics moderation team said the company wasn't featuring news from conservative outlets the same way they featured mainstream or liberal outlets. A deafening outcry from the right culminated in Zuckerberg calling on prominent conservatives to meet with him in Palo Alto.

For a time, the topic appeared to dissipate, amid new crises like the rise of fake news and the infiltration of Facebook by Russian trolls.

'Let me tell you something right now: Diamond and Silk is not terrorism.'

Representative Marsha Blackburn

But this week, suspected political bias at Facebook became a focal point once again, with Diamond and Silk at the epicenter. It first came up sparingly during Tuesday's hearing, when senators Ted Cruz and Ben Sasse pressed Zuckerberg on how the platform handles religious or traditionally conservative content. But it was far more central on Wednesday. Early in the hearing, Texas representative Joe Barton read a question he received—yes, through Facebook—from a constituent. "Please ask Mr. Zuckerberg why is Facebook censoring conservative bloggers such as Diamond and Silk?" he read. "Facebook called them unsafe to the community. That is ludicrous. They hold conservative views. That isn't unsafe."

"Congressman, in that specific case, our team made an enforcement error, and we've already gotten in touch with them to reverse it," Zuckerberg replied frankly, a defense he would return to repeatedly. Diamond and Silk later denied hearing from Facebook.

Later on, Marsha Blackburn of Tennessee also broached the topic of free speech. "Do you subjectively manipulate your algorithms to prioritize or censor speech?" she asked, prompting Zuckerberg to launch into a lengthy spiel about how certain posts, like terrorist content, have to be censored.

"Let me tell you something right now: Diamond and Silk is not terrorism," Blackburn retorted.

Conservative lawmakers had broader suppression concerns than just Diamond and Silk's status, and some did express serious qualms over Facebook's privacy problems. But the divergent lines of questioning underscored that the House remains divided in its view of Facebook and how to fix it—just as it is about almost every policy issue. Both sides seem unhappy, but they also seem woefully unprepared to work together to do anything about it, choosing instead to form protective circles around favored issues.

The conversation about ideological censorship on Facebook is a critical one. Even Pallone acknowledged that in an interview following the hearing, "I think it's a legitimate concern about purging content."

And yet, no conversation about censorship on Facebook is complete without mentioning how Facebook may have to give some countries the ability to curtail speech as the company pushes into places like China. Remarkably, over the course of five hours focused in large part on censorship, that never came up. On Wednesday, the free speech crusaders were mostly self-concerned. Listening to it all, you got the sense that Diamond and Silk's recent squabble has been a frequent topic of conversation in conservative circles on Fox News—or, you know, on Facebook.

Mr. Zuck Goes to Washington

Read more: