Nearly half of Democrats say they plan to vote by mail, while only one quarter of Republicans plan to do so, according to Reuters/Ipsos polling in August. Demand is driven in no small part by fear of infection from the coronavirus in public.

Counting mail ballots is often slower because officials must open thick envelopes, verify the ballots and validate voters’ identities, compared with the simpler, speedier process at a polling center where voters cast ballots in person…

Even some Republicans worry that Trump might exploit the uncertainty to cast doubt on the results if he ends up losing.

“The longer it takes to count absentee ballots, the more the narrative will take hold among Trump supporters and will be their ‘proof’ to question unfavorable election results,” said Dennis Darnoi, a Republican strategist based in Michigan, a state Trump won by less than a percentage point in 2016.