Edward Foley, director of the election law program at Ohio State University, came up with a hypothetical scenario in which Romney leads Ohio by 10,000 votes the day after the election — but there are 150,000 outstanding provisional ballots that must be examined. Ohio law gives voters 10 days, until Nov. 17, to provide officials with any information needed to show they are eligible to vote.
Under this scenario, if Obama were trailing, Foley said the president's legal team would try to "rescue" as many provisional ballots as possible and likely would head to court to obtain lists of voters' names they could contact. A similar fight took place in Washington state in a 2004 Senate race, he noted.
"It would not surprise me if there emerged a legal tussle over the availability of this information," Foley wrote in a recent article on the scenario.
That would mean Americans might not know the identity of their next president until well into November.
The provisional votes also could come up in Florida, the other big battleground state. University of Florida political science professor Daniel Smith noted than in the August primary about 22 percent of all provisional ballots were rejected by local canvassing boards. That too could become a source of court battles over the validity of such rejections, if the initial outcome in Florida is close enough.
"There's no question we're going to have a boatload of provisional ballots as well as overseas ballots that are not going to be tabulated until after Nov. 6," Smith said.
Sometimes evidence of election problems doesn't lead to litigation, even though it could. In 2004, Democratic nominee John Kerry initially refused to concede because of issues with provisional ballots and other problems in Ohio. But the day after the election, when Bush's lead in the state swelled to about 100,000 votes, it was clear a court fight wouldn't matter and the Democratic lawyers backed off.
It's all about the margin, said Johnson of the Miami-Dade Democrats, who said:
"Litigation can be expected unless there's a clear outcome on Election Day."
Braun reported from Washington.