WASHINGTON (AP):Mitt Romney would love an election like 1980, when Republicans carried 44 of the 50 states. President Barack Obama would be delighted with a repeat of 2008, when he trounced Senator John McCain with almost 100 electoral votes to spare.
What both dread is a recap of 2000, when it took more than a month and a Supreme Court ruling before Americans learned who would be their next president.
Even without a massive recount, plenty could go wrong on Tuesday.Here's a look at a few scenarios that could give Obama and Romney an election-day headache.
Popular vote vs electoral vote
It's happened a few times before, most recently in 2000. The candidate who wins the most votes overall comes in second in Electoral College votes - the ones that matter - and loses the election.
The Founding Fathers came up with the much-derided system as a compromise between a popular vote and letting Congress pick the president.
Attempts to abolish the Electoral College go back more than a half-century and seem to resurface every four years. But for now, it's here to stay. Proponents say doing away with the system would give areas with the densest population too much influence over the election.
So what are the chances this year of an electoral-popular split?
"It's not likely, but it's certainly possible. It's more likely than in most years, and more so than even a month ago," says Quinnipiac University pollster Peter Brown.
That's because Romney, in some national polls, is ever-so-slightly ahead, making it plausible he'll win the popular vote nationwide.
But many of the most competitive states, where the election will be decided, seem to be leaning in Obama's direction. That means it's possible Obama could lose the popular vote but still win the electoral vote, granting him a second term in the White House.
A 269-269 Electoral College tie
It takes 270 electoral votes to win. But what if both candidates win 269?
It's never happened. If it did, the newly elected House of Representatives would pick the president. Republicans control the House now, and are likely to hold on to their majority after election day.
What's more, instead of all 435 members getting a vote, each state delegation would get one vote. Since Republicans control many of the smaller states with fewer representatives, the GOP would have the advantage in this scenario.
But the Senate would get to pick the vice-president.
The Senate is in Democratic control and probably will stay that way. So would Senate Democrats send Joe Biden to be Romney's vice-president? Would Biden accept?
It's safe to assume both candidates are hoping we'll never have to find out.
Trouble at the polls
Long lines, problems with voting machines and challenges to voters' eligibility could all make for trouble at the polls. Hurricane Sandy, which knocked out power to millions across the East Coast, could increase the likelihood that things won't go as smoothly as planned.
A recent push by Republican officials in many states for tougher voting restrictions, such as requiring voters to show photo ID, could lead to a high number of provisional ballots, which voters are required to use if there's a question about their eligibility.
Those ballots are counted only if election officials determine the voters in question were eligible to vote. Different states have different rules on eligibility. It all makes it more likely there won't have a clear winner the night of the election.
Obama and Romney have scores of election lawyers on hand, ready to jump into action should the need arise.
Experts say it's most likely that litigation over the presidency would come down to Florida or Ohio, the states where Romney and Obama have campaigned the hardest.