This year, Florida could have 300,000 provisional ballots, said Michael McDonald, an election expert at George Mason University.
"You want to see chaos in Florida? There it is," McDonald said.
In Ohio, address changes were the biggest reason voters cast provisional ballots in 2008, said Ohio Secretary of State Jon Husted. Ohio voters cast about 207,000 provisional ballots in the 2008 presidential election — second only to California. About 130,000 of them were cast because voters moved and didn't update their voter registration, Husted said.
In 2004, the number of provisional ballots cast in Ohio was larger than Bush's margin of victory over Democrat John Kerry. Kerry didn't concede until the following morning, when the provisional ballot picture became clear.
In 2008, the number of provisional ballots cast in North Carolina was larger than Obama's margin of victory over Republican John McCain. The Associated Press didn't declare the state for Obama until the day after Election Day, though Obama had already won enough states to claim the presidency.
Husted said his office is trying to reduce the number of provisional ballots in Ohio by using change-of-address information from the Postal Service to send out more than 300,000 postcards to Ohio voters, reminding them to update their registration.
"If we can potentially reduce the number of ballots cast provisionally, then you lessen the likelihood that there will have to be a prolonged process as it relates to those ballots," Husted said. "Understand, a provisional ballot is a second chance because you didn't do it right the first time, meaning that you didn't update your address, you didn't bring in the proper form of ID, there's something that the voter didn't do at the onset that prevented them from voting a regular ballot."
Associated Press writer Connie Cass and AP election research coordinator Christina Bryant contributed to this report.
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