Voting by mail will face its biggest test since the onset of the coronavirus pandemic when seven states and Washington, D.C., hold primaries Tuesday.

All eight locales have encouraged residents to vote by mail, even as President Trump has criticized mail voting in recent tweets. Some states delayed their primaries due to the pandemic, then scrambled to change procedures and put personnel in place to process an expected surge in mailed ballots.

Tuesday’s presidential primaries—in Indiana, Maryland, Montana, New Mexico, Pennsylvania, Rhode Island, South Dakota and Washington, D.C.—offer little suspense since each political party already has a presumptive nominee. But state and local races are on ballots. And the voting will be an early test of how states might attempt to conduct elections if the virus remains a threat through the November general election.

Five states—Colorado, Hawaii, Oregon, Washington and Utah—conducted elections primarily by mail before the pandemic, with options for in-person voting and ballot drop-off sites as well.

Last-minute court rulings and partisan fighting spread confusion leading up to Wisconsin’s primary in April, and there were delays for absentee ballots and hour-plus waits at a reduced number of polling places in Milwaukee.