Could poorly marked ovals or boxes on mail ballots change election results?
Due to covid-19, more voters in Lexington County and elsewhere are expected to vote by mail. 
Marking and mailing ballots could increase errors that could be caught by a scanner or voting machine at the polls.
Experts say that's likely to produce more ballots with questionable marks requiring review. 
President Trump has repeatedly questioned the integrity of mail voting, and has challenged it in court.

Disputes could lead to legal challenges in battleground states like Michigan, Wisconsin and Pennsylvania.
Problems are already anticipated with late voting and late arrival of mailed ballots that may delay official results by weeks.
"This could be 2000's hanging chad," said Suzanne Almeida, interim director of the Pennsylvania 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."
Common Cause is working with election officials on 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.
In as many as 25 states, absentee ballots accounted for less than 10% of votes cast in 2016. 
Safeguards in election systems are geared to in-person voting.
Touchscreen voting machines are considered less secure by cybersecurity experts but do a better job than humans in recording votes and warning if voters try to vote twice.

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

This year, up to 75% of voters could use mail.
They will have to follow instructions carefully. If they make a mistake, they should contact their local election office and may need to request a replacement ballot.

Experts point to Georgia's experience after the June primary.
During vote counting, some counties reported what appeared to be valid votes that weren't flagged for review by the state's new high-capacity ballot scanners, which process large volumes of absentee ballots at once.
It turned out the scanner software was set to flag ballots with between 12% and 35% of an oval shaded. 
Anything more was automatically counted. 
Anything less was not.