Warren explained Saturday morning that her campaign purchased Facebook ads this week that purposefully included the lie that Zuckerberg had endorsed Trump’s re-election in order to highlight what she considered negligence on the part of the company’s handling of misinformation in political advertising (She notes later in the ad that Zuckerberg hadn’t actually endorsed Trump).

“We intentionally made a Facebook ad with false claims and submitted it to Facebook’s ad platform to see if it’d be approved. It got approved quickly and the ad is now running on Facebook,” she wrote. “They’ve decided to let political figures lie to you—even about Facebook itself—while their executives and their investors get even richer off the ads containing these lies.”

We intentionally made a Facebook ad with false claims and submitted it to Facebook’s ad platform to see if it’d be approved. It got approved quickly and the ad is now running on Facebook. Take a look: pic.twitter.com/7NQyThWHgO — Elizabeth Warren (@ewarren) October 12, 2019

Eric Reif, the campaign’s director of paid media, tweeted that “we put a little bit of money into a fairly obvious lie (which Facebook still shouldn’t have let us do!) to prove a point.”

A Facebook spokesperson said that the company believes political speech should be protected. “If Senator Warren wants to say things she knows to be untrue, we believe Facebook should not be in the position of censoring that speech,” the spokesperson said.

The company decided in the fall of 2018 that political ads and politicians would not be subject to the third-party fact-checking the company is using to combat misinformation. That policy has drawn a tremendous rebuke, particularly from Democrats in recent weeks after Nick Clegg, Facebook’s vice president of global affairs and communications, said in a speech last month that “It is not our role to intervene when politicians speak.”

He added that: “That’s why I want to be really clear today – we do not submit speech by politicians to our independent fact-checkers, and we generally allow it on the platform even when it would otherwise breach our normal content rules.”

Warren’s remarkably personal offensive against the platform and its high-profile CEO are yet another sign of the backlash against the company among many Democratic lawmakers since the 2016 election. Zuckerberg had been a darling of many Democratic lawmakers prior to the election, even hosting a town hall with former President Barack Obama in 2011 on Facebook’s campus.

But tensions between Facebook and Warren have been building for months, as the Democratic presidential hopeful campaigned to break-up tech companies like Facebook on anti-trust grounds. Facebook took down ads from Warren about dismantling the company — initially citing the use of the Facebook logo as a violation of its advertising policies — but later restored the ads “in the interest of allowing robust debate.” Warren’s campaign also purchased a “Break Up Big Tech” billboard in San Francisco last June while she campaigned there in another poke at Silicon Valley.

But the hostility spilled into public view in early October after The Verge published audio of the Facebook CEO telling employees over the summer that a Warren administration would likely “suck for us” and pledging to battle legal challenges from her potential Justice Department. “[I]f someone’s going to try to threaten something that existential, you go to the mat and you fight,” he said.

Warren and her campaign seized on the comments, seeming to revel in a public fight with one of the richest corporate executives in America. “It's clear: Silicon Valley billionaires are willing to sell out our democracy to protect their riches,” she wrote in an email to supporters on October 3rd.

In a Q & A session the next day that Facebook live-streamed to the public, a Facebook employee asked the CEO how he’d remain impartial in light of Warren’s criticisms.

“Let’s try not to antagonize her further,” he said.