ATLANTA (AP) — Two decades ago, Florida’s hanging chads became an unlikely symbol of a disputed presidential election. This year, the issue could be poorly marked ovals or boxes.

Amid the global coronavirus pandemic, more people than ever are expected to bypass their polling place and cast absentee ballots for the first time. Voters marking ballots from home could lead to an increase in the kinds of mistakes that typically would be caught by a scanner or election worker at the polls.

Experts say that’s likely to mean more ballots with questionable marks requiring review. That’s not necessarily a bad thing under normal circumstances, but President Donald Trump has repeatedly questioned the integrity of mail-in voting, and his campaign has already challenged aspects of it in court.

While ballots subject to review have historically represented a tiny portion of overall ballots, it’s possible disputes could arise and end up as part of a Florida-like fight, especially in battleground states like Michigan, Wisconsin and Pennsylvania.

“This could be 2000’s hanging chad in Pennsylvania,” said Suzanne Almeida, interim director of the state chapter of the nonpartisan watchdog Common Cause. “Potential challenges, delays in results, questions on which ballots count and who counts them — there are just a lot of questions, and that could open up Pennsylvania to a lot of uncertainty.”

The group is working with election officials statewide, emphasizing clear and consistent guidelines for dealing with questionable marks, such as when a voter circles a name or uses an X or a checkmark rather than filling in the oval — or even crosses out one selection and marks a second.

While all states perform ballot reviews and have rules related to voter intent, some have never seen anything like this year’s anticipated absentee ballot volume. In half the states, absentee ballots accounted for less than 10 percent of votes cast in 2016. Many could see half or more votes cast absentee this fall.

Safeguards built into the nation’s myriad election systems to help voters avoid ballot-marking problems are mostly geared toward in-person voting. Touchscreen voting machines — though considered less secure by cybersecurity experts — do a better job than humans in marking ballots and warning voters if they try to vote twice in the same race.

In-person voting by paper ballot typically involves filling in an oval or box next to a candidateás name. In most places, voters then feed the ballots into a scanner designed to reject so-called overvotes, like attempting to fix a mistake by crossing out a name and filling in the oval next to another candidate.

Such problems during in-person voting are easy to fix. Poll workers invalidate the ballot and give the voter a new one.

“But now, if most people are not voting with machines and are voting at home, they are not going to have that notification,” said Larry Norden, an elections expert with the Brennan Center for Justice.

This fall, as many as three in four voters could be voting on ballots received in the mail. That means following instructions carefully. If voters make a mistake, they should contact their local election office; it may mean requesting a replacement ballot.

Meanwhile, some election offices use bipartisan teams to review flagged ballots while others rely on staff or a local board. Citizens can observe, although rules vary on whether they can raise objections. Experts say if the process isn’t consistent with clear guidelines, there could be room for political or legal maneuvering.

Experts also note other concerns heading into November, primarily that ballots could be rejected for issues such as a missing signature or one that doesn’t match the one on file. In Pennsylvania, there are worries ballots could be rejected because voters don’t put them inside a “secrecy envelope” and then into a second, mailing envelope.

“All this doesn’t matter much, until it does,” said Mark Lindeman, co-director of Verified Voting. “It’s unusual for an election to hinge on ambiguously marked ballots, but it can happen.”

Copyright 2020 The Associated Press.