By Jeff Horwitz

Political groups are getting around Facebook Inc.'s system for blocking false political advertising by reposting ads found to violate its policies, exposing a loophole in the company's efforts to contend with misinformation.

Three political groups backing President Trump's re-election have adopted the tactic, repeatedly uploading with little or no alteration ads that Facebook had pulled down after its fact checkers judged them to be inaccurate, according to researchers on misinformation and a public archive Facebook maintains of ads run on its platform. Some of those reposted ads have been shown millions of times in swing states during the waning days of the U.S. presidential campaign, a period when Facebook has said it is taking extra care to stamp out misleading political ads.

The issue shows Facebook's continued challenges with enforcing its own policies across its massive platforms, especially on content that is politically divisive. Many on the left have said Facebook isn't aggressive enough on policing misinformation, while conservatives have accused Facebook and its fact checkers of bias and censorship.

American Principles Project, a conservative group based in Arlington, Va., ran ads on Facebook last month saying that former Vice President Joe Biden supports the loose collection of far-left activists known as Antifa, backs sex-change operations for children and supports legislation that would "destroy girl's sports" by allowing transgender athletes to compete in them.

Facebook removed the ads after its fact-checking partners including PolitiFact, an arm of the nonprofit Poynter Institute for Media Studies, deemed them to be either false or missing context. American Principles Project reposted versions of the ads with the same claims, but slight differences to the wording. The ads were targeted heavily at swing states, including Wisconsin and Michigan, according to Facebook's ad archive. In total, the reposted ads have been shown to Facebook users more than three million times, according to data gathered by Laura Edelson, a New York University researcher who studies political advertising online.

Terry Schilling, executive director of American Principles Project, said he had sought to alter the ads in ways that might avoid further action by fact checkers, such as by removing references to state-specific public policy issues.

"Frankly, the fact check organizations -- especially PolitiFact -- are extremely unhelpful in offering guidance on how to improve the accuracy of the ad. So in some cases we did a best guess," he wrote in an email to The Wall Street Journal.

Facebook acknowledged that it had failed to prevent some claims that had been previously determined misleading from returning to the platform. "We reviewed these ads and are taking action on those that violate our policies, while also working to improve how we find similar ads to those that were already rated," spokeswoman Andrea Vallone said.

Facebook over the weekend pulled down some of the reposted versions of the ads that the Journal asked about.

Aaron Scharockman, executive director of PolitiFact, said it has seen ads it judged false reposted, but that Politifact isn't equipped to track down all additional versions of a claim it deems false, and that Facebook determines what to remove. PolitiFact says it explains its decisions in its published fact checks.

The Democratic National Committee, which flagged some examples of the ad reposting to Facebook and the Journal, has complained to Facebook for more than a year about its failure to consistently enforce its fact checkers' decisions, Nellwyn Thomas, the DNC's chief technology officer, said in a written statement. She said that the loophole has allowed "blatant disinformation" to remain on the platform late into the U.S. presidential campaign.

The Republican National Committee didn't respond to requests for comment on whether it has seen examples of similar practices by anti-Trump groups.

Eric Wilson, a Republican political-technology strategist, said running the previously removed ads is a rational response to gaps in Facebook's enforcement system. "There's so much ad creation going on, and Facebook is so bad at enforcing their policies consistently," he said.

Facebook's political-ad policies have drawn criticism from both parties. Over the past year, Facebook has explained, defended and revised its rules, settling on an arrangement in which it doesn't fact-check ads from political campaigns themselves but does do so for political ads from individuals, businesses and political-action committees. The fact checks are done by a range of independent groups and designated news organizations.

Democrats have said that compromise gives a green light to misinformation campaigns. Republicans have said they are unfairly targeted.

Mr. Schilling said the ads from American Principles Project shouldn't have been fact-checked in the first place. He said his group plans to file a Federal Elections Commission complaint against Facebook after the election.

"Why not trust the American people to make the decision as to the accuracy of the ad?" he said. "What gives PolitiFact more credibility on gender identity issues than us?"

Facebook has announced other ad restrictions around the presidential campaign, including a ban on new political ads in the final week before Election Day, which Chief Executive Mark Zuckerberg said was designed to curtail false information in the campaign's waning days. Political advertisers, including from the Biden and Trump campaigns, said they have encountered ad glitches blocking approved ads that Facebook has since indicated it mostly solved.

The reposted ads that Facebook fact checkers judged false have sometimes had wide reach.

America First Action ran an ad saying that Mr. Biden plans to ban fracking, part of about $5.6 million spent on Facebook ads by the Republican PAC through a page managed by Parscale Strategy LLC, a digital advertising firm owned by Mr. Trump's former campaign director.

"Joe Biden's ban on fracking would put me and everybody I know out of work," a man described as a "Union Man" and Democrat says in the ad.

Facebook fact-checking partners including Lead Stories ruled this summer that the ad's claim isn't accurate.

Mr. Biden has said he doesn't intend to ban fracking, other than halting new drilling permits on federally owned land. He said in the second presidential debate that he plans to transition away from the oil industry to renewable energy over time.

After Facebook removed the ad, America First Action uploaded the same claim repeatedly, often with the exact same wording. Facebook's fact checkers eventually caught many of the repeats, but not before they gained wide distribution.

America First Action didn't respond to requests for comment.

According to data compiled by Ms. Edelson of NYU, the ads have been shown more than 2.4 million times to Facebook users in Pennsylvania since they were first removed for misinformation. More than one million of those impressions have been shown in the past week and a half.

"What's happening here is a failure of enforcement," said Ms. Edelson. She said it shouldn't be difficult for Facebook's artificial-intelligence technology to identify new uploads of an image, string of text or link that is associated with a fact check.

--Emily Glazer contributed to this article.

Write to Jeff Horwitz at Jeff.Horwitz@wsj.com

(END) Dow Jones Newswires

11-01-20 1729ET