Jessica Huseman for ProPublica:

While mail-in ballots seem like an elegant solution as the United States grapples with containing COVID-19, experts say slow-moving state and county governments, inconsistent state rules and limited resources to buy essentials such as envelopes and scanners could make it difficult to ramp up nationally to reach more than 200 million registered voters in the November general election. Among the possible downsides of a quick transition are increased voter fraud, logistical snafus and reduced turnout among voters who move frequently or lack a mailing address.

There is bipartisan consensus that mail-in ballots are the form of voting most vulnerable to fraud. A 2005 commission led by President Jimmy Carter and James A. Baker III — George W. Bush’s secretary of state — concluded that these ballots “remain the largest source of potential voter fraud.” Ballot harvesting scandals, in which political operatives tamper with absentee ballots that voters have entrusted to them, have marred recent elections in North Carolina and Texas.

Mail-in technology is also far more complex than a poll worker stuffing ballots into envelopes and opening them on return. In some cities with diverse populations, hundreds of types of ballots in multiple languages must be designed and directed to the appropriate voters in the correct precincts. Envelopes must be thick enough to protect voter privacy, and the paper thickness must be appropriate for scanners used to count ballots. When ballots are received, machines often open the envelopes and sort and tabulate the votes. These machines are expensive, and they generally take several months to order.