One of the most widely shared pieces of analysis published by conservative news and opinion site Breitbart after the election was an article headlined “Donald Trump Won 7.5 Million Popular Vote Landslide in the Heartland.” The article, published Nov. 15, was full of flat-wrong and deceptive information, including a fake electoral college map. Yet it spread like a virus, primarily across Facebook, and continues to deceive readers today even though the original article has since been corrected.

The premise of the article, written as a contrarian response to Hillary Clinton’s steadily increasing victory in the popular vote, was that if you take the 50 counties that voted most heavily for Clinton, excluded them from the total, and called the rest of the country the “heartland,” well then, yes, Trump had what it calls a “landslide in the heartland.”

Aside from that bit of analysis — which contains other fun errors of fact such as describing Bronx County, New York, as an “elite coastal county” — the most deceptive part of the story was its completely phony electoral map, which continues to be shared on Facebook even after the Washington Post called it out as wrong and the original article was corrected.

The article continues to be shared with the uncorrected image, offering a case study in how easy it is to get fake news to spread and how hard it is to stamp it out.

Breitbart’s false map is not anomalous; fake news proliferated rapidly this election cycle, in part because it does so well on Facebook. A recent BuzzFeed News analysis found that on Facebook, the most-trafficked stories from fake news sites (“WikiLeaks CONFIRMS Hillary sold weapons to ISIS…”) vastly outperformed those from “mainstream” media publications like the New York Times (“I ran the C.I.A. Now I’m Endorsing Hillary Clinton”).

The contrarian headline and neat symmetry of the illustration made the fake Electoral College map irresistible share-bait on Facebook. John Philip Riffice, a Trump voter from the Chicago metropolitan area who shared the article on Facebook, told VICE News that he almost instantly regretted it.

“I posted it and realized, wait it a minute, there’s some blue missing here. Hillary won Illinois, and a few other states and what not,” Riffice said in a phone interview. “I don’t want to post anything that I know is blatantly false, and inadvertently I posted that one. So in retrospect, that [Breitbart article] is false and I wish I hadn’t done it.”

In a phone interview with VICE News, Breitbart Washington Political Editor Matthew Boyle said he didn’t know where the fake map came from, but acknowledged attaching it to the story was a mistake and that “we clearly we updated the map after we faced criticism.”

As to why the false version is still circulating on Facebook, “Our Facebook is handled by other people. To be honest with you, I don’t even read our Facebook,” Boyle said. “But specifically I think the story is sound … it’s not a new argument to point out that there are two Americas out there.”

So far the initial Facebook post — which still features the fake map — has garnered about 35,000 shares, 59,000 likes and 2,400 comments. The map has been shared thousands of times on Twitter as well, including by conservative pundit and rumored White House press secretary candidate Laura Ingraham.

“I think this is a significant issue; we have a premium on accuracy. We strive to make sure we have accurate reporting,” Boyle said. “Yes, we’re open about our political beliefs, but the most important thing to us is ensuring that we have accurate information and illustrations on our website.”

The writer of the article, Breitbart contributor Michael Patrick Leahy, appears to be self-employed and previously worked as an “activist” for the Republican National Committee, according to public records. The RNC did not respond to a request to confirm Leahy’s employment history. Reached by phone, Leahy declined to comment on the article the day after it was published, but told VICE News we would be “very interested” in a follow-up article coming soon.

Like a lot of modern publishers that have grown in prominence over the past few years, Breitbart reaches its audience primarily through Facebook. According to data from the analytics firm NewsWhip, Breitbart was the fourth-most engaged (meaning the sum of likes, shares and comments) publisher on Facebook on Election Day, behind NBC, the Huffington Post, and USA Today. We should add that, like almost all web publishers, VICE News — and VICE generally — receives a significant chunk of traffic from Facebook.

“We see that Facebook drives anywhere between 30 to 40 percent of traffic,” said Dan Valente, chief data scientist at web analytics firm Chartbeat. “My guess is that [Breitbart is] on the higher end of Facebook publishers, because they get more traffic from Facebook than other sources because of the content that they post.”

Mark Zuckerberg and Facebook initially denied that fake news had any impact on the election (Zuckerberg called such thinking “a crazy idea”), but eventually Zuckerberg promised to deal with fake news on his platform. Still, he maintained that Facebook does “not want to be arbiters of truth ourselves, but instead rely on our community and trusted third parties.”

Independently auditing Zuckerberg’s announced fixes will be difficult because unlike, say, Twitter, Facebook shares an extremely limited amount of data with outsiders. Additionally, these changes don’t alter the fundamental architecture of the service, which allows misinformation to thrive.

“By design, Facebook emphasizes the sharing aspects of the site — sharing, liking, commenting, and so forth. It deemphasizes sorts of activity that doesn’t happen on Facebook, like reading the article,” said Washington State University professor Mike Caufield. “At some level it becomes about, ‘How fast do people share this?’ So to expedite sharing, you do have to plug in the anger and the outrage. And sites have learned to design around that.”

Google recently said it would remove highlighted news articles from the top of desktop search results altogether in order to root out fake news. But Facebook’s uniform design gives equal weight to real news and fake news, a concern for a company that has tweaked its service to make itself a “perfect personalized newspaper” for users.

“The entire structure of Facebook is not set up as a news-sharing platform, but as a headline and image-rating platform,” Caufield said.

And while creating headlines and content that plays well on Facebook is part of nearly every publisher’s toolkit at this point, Breitbart perhaps has a natural advantage.