In 2008, more than 200,000 provisional ballots were cast in Ohio. Experts say more than 300,000 could be cast in this election.

"If the margin of victory for either candidate is less than the outstanding number of provisional ballots, we won’t actually know who won Ohio and perhaps the presidency until Nov. 17," said Michael Waldman, president of the Brennan Center for Justice at the New York University School of Law.

Ohio’s system for verifying registered voters has also come under fire after 33,000 applicants for absentee ballots were wrongfully denied their requests. They were told that they were not registered to vote when, in fact, they were.

State officials blamed the oversights on a data-sharing problem with the state Department of Motor Vehicles.

Last week, a state voter education organization notified Husted’s office that nearly 900 voters in the Cleveland area and an estimated 6,000 statewide may have been denied absentee ballots because of incomplete data checks by local elections officials.

In response, Husted sent a separate directive last week urging county election boards to try "at least one (of four) additional search criteria" if an applicant’s name didn’t appear on the list of registered voters.

In New Jersey, voters dislocated by Hurricane Sandy can vote anywhere in the state and absentee ballots are being distributed in homeless shelters as a result of a directive from New Jersey Lt. Gov. Kim Guadagno.

Storm victims in New Jersey can vote via the Internet but only if they have power and access to scanners or fax machines to send the ballots back by email, said Lawrence Norden, deputy director of Brennan’s Democracy Program.

Up to now, state law only permits military and overseas voters to cast ballots by email or fax. Unlike those voters, however, the storm directive doesn’t require displaced people to provide a paper backup to prevent vote fraud.

Penny Venitis, a Rutgers University law professor, called it “critical to have a paper backup.”

Internet voting is “inherently insecure” and “email voting is the most insecure form of Internet voting,” said Andrew Appel, a computer science professor at Princeton University who joined Venitis and two other election experts on a conference call with reporters. New York has no plans to follow New Jersey’s lead.

While 250,000 of the 1 million New York voters hit hard by the storm will have to change polling stations, Doug Kellner, the New York State Board of Elections co-chairman, said that shifting to email wouldn’t be fair to voters “who are not on the right side of the digital line and would not have backup electricity to run a printer” so that they could print and mark the ballot.

In Florida, meanwhile, Miami-Dade Elections Supervisor Penelope Townsley stood before about a dozen television cameras to reassure the public that Election Day would go smoothly.

“I’d like the voters of Miami-Dade County to be confident that we are prepared," she said.

Patricia Mazzei of the Miami Herald contributed.