In August, a video posted on social media by a Florida woman named Tina Brown outlined what she claimed were potential hazards with mail-in ballots. She said envelopes for registered Democratic voters included a D in the bar code, while envelopes for Republicans contained an R. She then asserted that a left-leaning mail carrier could use the identifiers to suppress Republican votes.

But Brown's video omitted the fact that the ballots were for separate party primaries, leaving the impression that they were for the general election in November.

Even so, the Facebook video gained 175,000 views from mid-August through late September and inspired similar false content across Facebook, Twitter, YouTube and TikTok. That the bogus claim spread so easily across the internet highlights the challenges facing social media companies attempting to crack down on false information even as a torrent of misinformation continues.

It also shows the challenges facing government officials, who are trying to manage a presidential election in the midst of a pandemic and a sharp uptick in online posts about mail-in voting. Volume has surged 91% in recent months, and much of it involves false information, including that mail-in ballots won't count and that mail-in voting creates fraud, said research from Clemson University.

Such falsehoods have been fueled by President Donald Trump, researchers said. In last Tuesday's presidential debate, he cited unproven allegations about fraud associated with mail-in ballots as a reason for telling his supporters to "go into the polls and watch very carefully" — a claim that cast doubt on the integrity of the election.

A Harvard University working paper — which analyzed more than 5 million tweets, 75,000 Facebook posts and 55,000 media stories online — found that the Trump campaign and Fox News were the driving force behind false claims about mail-in ballots, with social media playing a supporting role. Clemson found that Trump's Twitter account has been the most influential in that online conversation.

Experts believe that vote-by-mail conspiracies would likely be relegated to the fringes were it not for Trump's use of his Twitter feed as well as TV appearances, rallies, news conferences and the presidential debate to malign mail-in ballots.