In the final stretch of the 2020 campaign, right-leaning news sites with millions of readers have published dozens of false or misleading headlines and articles that effectively back unsubstantiated claims by President Donald Trump and his allies that mail-in ballots threaten the integrity of the election.

The Washington Examiner, Breitbart News, the Gateway Pundit and the Washington Times are among the news outlets that have posted articles with headlines giving weight to the conspiracy theory that voter fraud is rampant and could swing the election to the left, a theory that has been repeatedly debunked by data.

On Sept. 25, Gateway Pundit posted an article headlined "EXCLUSIVE: California Man Finds THOUSANDS of What Appear to be Unopened Ballots in Garbage Dumpster — Workers Quickly Try to Cover Them Up — We Are Working to Verify." The envelopes turned out to be empty and discarded legally in 2018. Gateway Pundit later updated the headline, but not before its original speculation had gone viral.

The Right Scoop published an article Oct. 7 headlined "DESTROYED: Tons of Trump Mail-in Ballot Applications SHREDDED in Back of Tractor-trailer Headed for Pennsylvania." The material was actually printing waste from a direct-mail company. The publication later changed the headline to reflect that the claim had been debunked.

Another right-wing site, Daily Wire, posted a Sept. 24 article about ballots in Pennsylvania under the headline "FEDS: Military Ballots Discarded in 'Troubling' Discovery. All Opened Ballots Were Cast for Trump." Headlines on the same issue in the Washington Times were similar: "Feds Investigating Discarded Mail-in Ballots Cast for Trump in Pennsylvania" and "FBI Downplays Election Fraud as Suspected Ballot Issues Found in Pennsylvania, Texas." A Washington Times opinion piece on the matter had the headline "Trump Ballots in Trash, Oh My."

Several days after the reports, neither Daily Wire nor the Washington Times appeared to follow up with articles on the announcement from Pennsylvania's elections chief that the discarded ballots were a "bad error" by a seasonal contractor, not "intentional fraud." Trump cited the discarded Pennsylvania ballots several times as an example of fraud, including in last month's presidential debate.

Major polls have shown Trump lagging the Democratic presidential nominee, Joe Biden, in an election that will have significantly more people than usual voting by mail because of the coronavirus. False claims about mail-in voting have been a staple of the president's campaign. At last month's debate, he claimed without evidence, "This is going to be a fraud like you've never seen."

In June, Trump posted on Twitter that "Mail-In Ballots will lead to a RIGGED ELECTION!" He linked to a Breitbart article that included a transcript of Attorney General William Barr's telling Fox News host Maria Bartiromo that voting by mail "absolutely opens the floodgates to fraud."

In August, the New York Post published an article that relied on one anonymous source, identified as a Democratic operative, who claimed that he had engaged in voter fraud for decades. The Blaze, Breitbart, Daily Caller, FoxNews.com and the Washington Examiner posted their own versions of the article. It was also promoted by Donald Trump Jr. and his brother Eric, the Trump campaign's communications team, the "Fox & Friends" television program and Tucker Carlson's Fox News show, according to a recent Harvard University study.

The Harvard researchers described a "propaganda feedback loop" in right-wing media. The authors of the study, published this month through the school's Berkman Klein Center for Internet and Society, reported that popular news outlets, rather than social media platforms, were the main drivers of a disinformation campaign meant to sow doubts about the integrity of the election.

So far in October, Breitbart has published nearly 30 articles with the tag "voter fraud." The president has posted links to several Breitbart articles on Twitter, including one in August in which a Republican-appointed poll challenger estimated that up to 20,000 absentee primary ballots had been improperly counted in Detroit, a city "known for voting heavily Democrat," the article said. The Detroit News later reported that election officials in Michigan said the problems "weren't examples of fraud and don't call into question the integrity of the results."

As the country faces a third wave of COVID-19 cases, tens of millions of Americans plan to mail their ballots, and more than 25 states have expanded access to universal mail voting. The voting system, stressed by greater demand, has struggled in places with ballots sent to incorrect addresses or improperly filled out. But intentional voter fraud is extremely uncommon and rarely organized, according to decades of research.

That's true even though specific totals vary depending on the source. Among the billions of votes cast from 2000 to 2012, there were 491 cases of absentee ballot fraud, according to an investigation conducted at Arizona State University's journalism school. Election experts have calculated that, in a 20-year period, fraud involving mailed ballots has affected 0.00006% of individual votes, or one case per state every six or seven years.

In June, the Washington Post and the nonprofit Electronic Registration Information Center analyzed data from three vote-by-mail states and found 372 possible cases of double voting or voting on behalf of dead people in 2016 and 2018, or 0.0025% of the 14.6 million mailed ballots.

Voting by mail under normal circumstances does not appear to give either major party an advantage, according to a study this spring by Stanford University's Institute for Economic Policy Research. But many conservative outlets have promoted the idea that fraud involving mailed ballots could tip the scales in favor of Democrats.