"As we’ve explained, there is no evidence to support Trump’s overall claim that 'mailed ballots are corrupt,' as he said in April," FactCheck reports. "Voting experts told us the president is exaggerating when he says mail ballots are 'fraudulent in many cases.' While the instances of voter fraud via mail-in or absentee ballots are more common than in-person voting fraud, the number of known cases is relatively rare."
FactCheck delves into more specific false, misleading or unfounded claims Trump has made about absentee vs. universal mail-ballot voting, Michigan and California's mail-voting systems, and the notion he has promoted that mail-in ballots will be printed overseas, resulting in a rigged election.
It is worth noting that mail-in voting involves the U.S. Postal Service, a financially ailing entity Trump has long criticized. "Members of Congress and state officials in both parties rejected the president’s suggestion and his claim that mail-in ballots would result in widespread fraud," Michael Shear, Hailey Fuchs and Kenneth Vogel report for The Washington Post. "But they are warning that a huge wave of ballots could overwhelm mail carriers unless the Postal Service, in financial difficulty for years, receives emergency funding that Republicans are blocking during negotiations over another pandemic relief bill." Democrats have decried recent money-saving measures by new Postmaster General Louis DeJoy, saying he is laying the groundwork for mailed-ballot disputes. He denies it.