The claim that election fraud is a major concern with mail-in ballots has become the central threat to election participation during the Covid-19 pandemic and to the legitimacy of the outcome of the election across the political spectrum. President Trump has repeatedly cited his concerns over voter fraud associated with mail-in ballots as a reason that he may not abide by an adverse electoral outcome. Polling conducted in September 2020 suggests that nearly half of Republicans agree with the president that election fraud is a major concern associated with expanded mail-in voting during the pandemic. Few Democrats share that belief. Despite the consensus among independent academic and journalistic investigations that voter fraud is rare and extremely unlikely to determine a national election, tens of millions of Americans believe the opposite. This is a study of the disinformation campaign that led to widespread acceptance of this apparently false belief and to its partisan distribution pattern. Contrary to the focus of most contemporary work on disinformation, our findings suggest that this highly effective disinformation campaign, with potentially profound effects for both participation in and the legitimacy of the 2020 election, was an elite-driven, mass-media led process. Social media played only a secondary and supportive role.