Eight states and the District of Columbia are holding primary elections on Tuesday, the biggest test yet of officials' readiness to manage a surge of mail ballots and the safety risks of in-person voting during the coronavirus outbreak.
The largest day of balloting since the pandemic began will serve as a dry run for the Nov. 3 general election, offering a glimpse of the challenges ahead on a national scale if that vote is conducted under a lingering threat from Covid-19.
The voting in Tuesday's elections could be complicated in some areas by massive protests following the death of an African-American man in police custody in Minnesota last week. Philadelphia's mayor said a city curfew would not be enforced until 30 minutes after polls close, and voters and poll workers in Washington will be exempt from that city's curfew, the mayor said.
Four of the states voting on Tuesday - Pennsylvania, Indiana, Maryland and Rhode Island - delayed their nominating contests from earlier in the year to avoid the worst of the coronavirus outbreak that has killed more than 104,000 people in the United States.
All of the states, which also include Iowa, Montana, New Mexico and South Dakota, have encouraged or expanded mail-in balloting as a safe voting alternative.
That has led to record numbers of mail-in ballots requested or cast in many states, along with an explosion of questions, confusion and reports of ballot applications delayed or lost.
Most states also will sharply reduce the number of in-person polling places as officials struggle to recruit enough workers to run them.
"We will have a lot of clarity after June 2 about what needs to be fixed for November, and we're hoping we can come up with some clear practical solutions," said Suzanne Almeida, acting director of government watchdog Common Cause Pennsylvania.
Counting the flood of mail-in ballots could delay the announcement of results, officials said. In Pennsylvania, Governor Tom Wolf extended the deadline for receiving mailed ballots postmarked by June 2 to June 9 in six counties, including Philadelphia.
The primaries come amid a partisan brawl over voting by mail, which Democrats support as a safe way to cast a ballot and Republican President Donald Trump condemns as ripe for fraud. Numerous studies have found little evidence of voting fraud tied to mail-in ballots.
Former Vice President Joe Biden has essentially wrapped up the Democratic presidential nomination to face Trump in November, but seven of the states also will have primaries for state and congressional offices.
Among the top races to be decided on Tuesday will be a Republican congressional primary in Iowa. US Representative Steve King, who has a long history of making racially charged remarks, faces a stiff re-election challenge after being largely abandoned by party leadership.