‘Absentee ballots remain the largest source of potential voter fraud.” That quote isn’t from President Trump, who criticized mail-in voting this week after Wisconsin Democrats tried and failed to change an election at the last minute into an exclusively mail-in affair. It’s the conclusion of the bipartisan 2005 report of the Commission on Federal Election Reform, chaired by former President Jimmy Carter and former Secretary of State James Baker III.

Concerns about vote-buying have a long history in the U.S. They helped drive...