WASHINGTON (AP) — Long voting lines on Election Day aren’t unusual or necessarily a sign of that something nefarious is afoot.

They’re often the product of something as simple as heavier-than-expected turnout for an important election like Tuesday’s presidential, congressional and other races.

Long lines also develop when there aren’t enough voting machines — either because some have malfunctioned or there just aren't enough of them to comfortably manage the turnout — or when poll workers don't show up for their assignments, leading to understaffing.

This year, polling places are putting social distancing measures in place because of the coronavirus pandemic, with voters who are in line encouraged to keep at least 6 feet (1.83 meters) apart — automatically making for longer lines.

Long lines materialized in many counties in many states during the past few weeks of early in-person voting because the early turnout was so heavy.

Nearly 100 million Americans voted early.

One scenario that could complicate Tuesday's voting: voters who decide to show up at the polls after getting a ballot in the mail, or not receiving one they requested.

Voters with mailed ballots can change their minds and choose instead to vote in person. However, poll workers will have to take extra steps to make sure the person won't vote twice, which is illegal. The same applies to someone who shows up to vote, claiming not to have received a ballot.

Many such cases could contribute to long lines because of the time needed to resolve these and other issues.

On the flip side, the high number of people who have already voted early — whether in-person or by mail — could turn out to be a benefit on Tuesday.

“There is a good chance that the voting on Election Day may be kind of light if a high percentage of the vote is already in,” said Tom Verdin, AP's national editor for state government.

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This story is part of a series dedicated to answering commonly asked questions from AP’s audience about the 2020 U.S. presidential election.