New laws in competitive states like Virginia, Florida, Pennsylvania and Wisconsin could leave the outcome of the presidential election in doubt — if the vote is close — while new laws in Kansas, Mississippi, South Carolina and Tennessee could delay results in state or local elections.

Some new laws requiring voters to show identification at the polls are still being challenged in court, adding to the uncertainty as the Nov. 6 election nears.

“It’s a possibility of a complete meltdown for the election,” said Daniel Smith, a political scientist at the University of Florida.

Voters cast provisional ballots for a variety of reasons: They don’t bring proper ID to the polls; they fail to update their voter registration after moving; they try to vote at the wrong precinct; or their right to vote is challenged by someone.

These voters may have their votes counted, but only if election officials can verify that they were eligible to vote, a process that can take days or weeks. Adding to the potential for chaos: Many states won’t even know how many provisional ballots have been cast until sometime after Election Day.

Voters cast nearly 2.1 million provisional ballots in the 2008 presidential election. About 69 percent were eventually counted, according to election results compiled by The Associated Press.

Provisional ballots don’t get much attention if an election is a landslide. But what if the vote is close, as the polls suggest in the race between President Barack Obama and Republican Mitt Romney?

Most of today’s voting nightmares go back to Florida in 2000, when the results of balloting and thus the winner of the presidential contest were not known for weeks after Election Day. Questions about recount irregularities and the validity of ballots with hanging chads — paper fragments still attached to punch-card ballots — preceded the eventual declaration that George W. Bush had won the state by 537 votes and was the next president.

“In a close election, all eyes are going to be on those provisional ballots, and those same canvassing boards that were looking at pregnant chads and hanging chads back in 2000,” Smith said. “It’s a potential mess.”

The federal election law passed in response to the 2000 presidential election gives voters the option to cast a provisional ballot, if poll workers deny them a regular one. Voter ID laws could slow the count even more.

In Virginia and Wisconsin, voters who don’t bring an ID to the polls can still have their votes counted if they produce an ID by the Friday following Election Day. Pennsylvania’s law gives voters six days to produce an ID. The Wisconsin and Pennsylvania laws are being challenged in court.

In Ohio, which has competitive races for both president and the Senate, provisional voters have up to 10 days following the election to bring an ID to the county board of elections.

If voters in Florida don’t bring an ID to the polls, they must sign a provisional ballot envelope. Canvassing boards then will try to match the signatures with those in voter registration records, a process that conjures up images of the 2000 presidential election in Florida.

“Americans have gotten used to the expectation that you could turn on the TV and you would know that night who won the election, even after Florida in 2000,” said Edward B. Foley, a law professor at Ohio State University. “But this could be an election in which we don’t know the answer for several days.”

Florida could see a big increase in provisional ballots because the state has tightened its change-of-address requirements. This year, voters who move from one county to another in Florida without updating their voter registration will have to cast provisional ballots. In previous elections, they could change their address on Election Day and cast a regular ballot.

Four years ago, Florida voters cast about 36,000 provisional ballots. About half of them were eventually counted, though the percentages varied greatly from county to county.

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.”

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Associated Press writer Connie Cass and AP election research coordinator Christina Bryant contributed to this report.

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