Vote-by-mail worries: A ‘leaky pipeline’ in many states

FILE - In this July 30, 2020, file photo, boxes for illegal and legal vote-by-mail ballots are shown as the the Miami-Dade County canvassing board meets to verify signatures on vote-by-mail ballots for the Aug. 18 primary election at the Miami-Dade County Elections Department in Doral, Fla. Never in U.S. history will so many people exercise the right on which their democracy hinges by marking a ballot at home. (AP Photo/Lynne Sladky, File)

Vote-by-mail ballots are shown in a sorting tray, Wednesday at the King County Elections headquarters in Renton, Wash., south of Seattle. (AP Photos/Ted S. Warren)

Vote-by-mail ballots are shown in sorting trays, Wednesday.

BOSTON — Brace yourself for what’s expected to be the first U.S. presidential election conducted mostly by mail. It could be messy.