After rampant fake news on Facebook dominated much the narrative about the 2016 election, CEO Mark Zuckerberg told Congress that the company “made mistakes” regarding its handling of the issue. But a recent change to the company’s policy that now allows falsehoods in political ads—a reversal of its prior stance—and Democratic presidential candidate Elizabeth Warren (D-MA) is calling Zuckerberg out with a fake news ad of her own.

“Breaking news,” the post says, “Mark Zuckerberg and Facebook just endorsed Donald Trump for re-election. You’re probably shocked, and you might be thinking, ‘How could this possibly be true?’ Well, it’s not. (Sorry.) But what Zuckerberg has done is given Donald Trump free rein to lie on his platform — and then to pay Facebook gobs of money to push out their lies to American voters.”

It’s a brilliantly clever way of using Zuckerberg’s own policy against him. On Twitter, Warren said of the ad: “Facebook changed their ads policy to allow politicians to run ads with known lies,” she wrote, adding, “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 explained that the ad was a test of how much a politician can lie on Facebook “to see just how far” the policy goes.

As writer Judd Legum pointed out on Twitter, Facebook strictly prohibited “deceptive, false, or misleading” content in ads on the platform up until September of this year when they removed that wording from their ads policy.

Also since October 2016, Facebook has had a “newsworthiness” exemption, allowing posts deemed newsworthy to be exempt from its community standards against hate speech or cruel and insensitive speech. “We’re going to begin allowing more items that people find newsworthy, significant, or important to the public interest—even if they might otherwise violate our standards,” Facebook said at the time. And the company recently announced that it “will treat speech from politicians as newsworthy content that should, as a general rule, be seen and heard.” This combined with removing the part of its policy prohibiting misleading content in advertising, essentially created a loophole for lies in political ads.

“We rely on third-party fact-checkers to help reduce the spread of false news and other types of viral misinformation, like memes or manipulated photos and videos,” Facebook VP of Global Affairs and Communications and former UK member of parliament Nick Clegg wrote in a blog post explaining the decision. “We don’t believe, however, that it’s an appropriate role for us to referee political debates and prevent a politician’s speech from reaching its audience and being subject to public debate and scrutiny. That’s why Facebook exempts politicians from our third-party fact-checking program.”

This is a different tune from what Zuckerberg told Congress in 2018 when he said, “As Facebook has grown, people everywhere have gotten a powerful new tool to stay connected to the people they love, make their voices heard, and build communities and businesses. But it’s clear now that we didn’t do enough to prevent these tools from being used for harm as well. And that goes for fake news, for foreign interference in elections, and hate speech, as well as developers and data privacy.”

Warren has long been a critic of the tech giant, vowing to break up it and other Silicon Valley behemoths. Zuckerberg even recently told employees that a Warren presidency would “suck” for the company.

And Warren is showing no signs of backing down. “Facebook already helped elect Donald Trump once through negligence,” she said. “Now, they’ve changed their policy so they can profit from lies to the American people. It’s time to hold Mark Zuckerberg accountable.”