Press Secretary Sarah Huckabee Sanders announced on Twitter Saturday that she and her family had been asked to leave the Red Hen, a small restaurant in Lexington, Virginia. The Red Hen's co-owner, Stephanie Wilkinson, reportedly asked Sanders to leave because of her involvement in Trump administration policies like separating migrant children from their parents. Word of the incident quickly spread across the internet and on Monday, President Donald Trump lobbed an insult at the Red Hen, alleging that the restaurant’s exterior is "dirty."

But the majority of the backlash against the Red Hen came on a different platform: Yelp. Many of the press secretary's supporters spent the weekend vandalizing the restaurant's page by leaving thousands of fraudulent one-star reviews. Others who agreed with Wilkinson's decision responded by writing retaliatory five-star reviews, turning Yelp into an unwilling platform for political speech. In essence, Yelp became a battleground—and not for the first time. For years, crowd-sourced review sites like Yelp and TripAdvisor have been manipulated by trolls, paid reviewers, and politically enraged citizens. But we rarely consider how sites like Yelp fight back—and what their tactics mean for businesses and users.

This is far from the first time that Yelp has experienced a surge in vandalism in response to the news cycle. In 2012, for example, trolls famously defaced a pizza parlor’s page after the restaurant’s owner posted a picture of himself hugging former President Barack Obama. The issue comes up enough that Vince Sollitto, Yelp’s senior vice president for corporate communications, penned a blog post in 2016 explaining the company’s strategy for when similar incidents happen.

As Sollitto explains, Yelp doesn’t display every review left for a business in chronological order; the company uses an algorithm to sort reviews according to a number of signals, including whether they may be biased or fraudulent. Reviews that get sorted out also don’t contribute toward a business’s overall rating.

In situations like the Red Hen’s, Yelp deploys what it calls an Active Cleanup Alert, a pop-up that encourages users to discuss a business on Yelp’s discussion forums rather than leaving a review; it also warns them that fake ones will be removed. While the alert is active, Yelp employees work to identify and remove what they believe are fraudulent reviews. Again, Yelp blogged about this policy in 2016 and Active Cleanup Alerts were created the year before.

So in theory, when a local business becomes part of a national controversy, Yelp has an established strategy to deal with the fallout. In reality, the Red Hen’s Yelp page remains a mess. It had more than 15,000 reviews at the time of writing and the restaurant’s overall rating is down to 1.5 stars, from nearly five stars several days ago. People have attacked unaffiliated restaurants with similar names, and some have baselessly accused Red Hen of being run or owned by pedophiles.

Part of the problem, as Motherboard points out, is that Yelp doesn’t require reviewers to verify that they’ve actually visited a business, making it easy to turn the platform into a place for protest.

To be fair, Yelp has to manage more than 155 million reviews, according to the company, and not all of its resources can realistically be dedicated to defending one restaurant. Yelp’s moderators are also up against people like conservative activist Charlie Kirk, who encouraged his more than 600,000 Twitter followers Sunday to leave 100,000 additional reviews on the Red Hen’s page. TripAdvisor, for its part, temporarily stopped allowing reviews to be posted at all.