While in-person voting looks safer than expected, mail-in voting looks more dangerous—not because of fraud, but because of human error and partisan politics.

Mail votes require several steps, and different steps in different locations, including postmarking the ballots, signing in various places, and using the proper number of envelopes. For that reason, it can confuse first-time voters, and even experienced voters used to queuing at local high schools. Two studies of the 2018 midterm elections in Florida and Georgia found that young and minority voters are especially likely to have their mail ballots rejected. (Both those voting groups skew Democratic.)

With millions of people voting by mail for the first time this year, experts expect more errors—and more rejected ballots. In the 2020 primaries, more than 550,000 mail and absentee ballots were disqualified, a much higher number than four years ago. The problem is especially severe in some swing states. More than 23,000 mailed ballots were rejected in the presidential primaries in Wisconsin—more than Donald Trump’s margin of victory in that state in 2016. Deep-blue districts have had the same problem: New York City alone threw out more than 84,000 ballots this primary season.

In November, states should be more prepared for the onslaught of mail ballots than they were this spring. “We’ve remedied several of the problems we had earlier this year, including new rules to allow election clerks to avoid overwork in November, to avoid bookkeeping errors,” Jocelyn Benson, Michigan’s secretary of state, told me.