US President Barack Obama and Republican Mitt Romney capped an aggressive, deeply negative and vastly expensive campaign and were awaiting the decision of voters Tuesday in an election that left Americans the choice of starkly different visions for the country's future.
At stake at the end of Election Day were overwhelmingly different approaches for healing the ailing US economy, polar opposite views on social issues from abortion rights for women to how to deal with immigration and the conduct of American foreign and military policy across the globe.
While nationwide polls going in to Election Day showed Obama and Romney virtually tied, the president was seen as holding slim leads in many of the nine swing states - Ohio chief among them - that were likely to determine the winner.
Exit polls found most voters saying the economy is the top issue facing the nation with three-fourths calling it poor or not so good.
The swing states were the focus of attention on Tuesday night because the president is chosen in state-by-state contests, not according to the nationwide popular vote. The candidate who wins a state - with Maine and Nebraska the exceptions - is awarded all of that state's electoral votes, which are apportioned based on representation in Congress. Going into voting Tuesday, an Associated Press analysis of the states showed Obama with 243 electors in his column, 206 for Romney.
As polls began closing in the eastern US, the Associated Press called the race in reliably Democratic Vermont for Obama and for Romney in overwhelmingly Republican Kentucky - both expected outcomes.
But with so many swing-state electors still up for grabs, there was a possibility of a repeat of the 2000 election, when the winner, George W Bush, was not known for weeks after a protracted recount in Florida and a Supreme Court decision. A narrow victory for either candidate this time is sure to deepen polarisation and leave the winner without a strong mandate to face mounting problems - notably, the "fiscal cliff" of higher taxes and deep automatic cuts in spending that loom in January if Republicans and Democrats in Congress cannot reach an accord on US finances.
Most eagerly awaited were results in Ohio and four other swing states also in the eastern section of the United States - Florida, North Carolina, Virginia, and New Hampshire. Moving west, the polls will then close next in the swing states of Wisconsin and Iowa in the Central time zone, then in Colorado and Nevada. The race was seen as so close that the outcome might not be known until the early hours of Wednesday or later.
Obama played basketball in a gymnasium near his home on Chicago's south side Tuesday afternoon as millions of Americans waited in long lines to cast their ballots. Earlier he was met with applause and tears from volunteers as he entered a campaign office before picking up a phone to call voters. He congratulated Romney on a "spirited campaign" and told reporters he's "confident we've got the votes to win, but it's going to depend ultimately on whether those votes turn out."
Romney and family were at his home near Boston to wait for the results after making two last campaign stops Tuesday with running mate Paul Ryan in Ohio and Pittsburgh, Pennsylvania. That state was thought to have been solidly in the Obama column but one where the Republican challenger had opened a last minute drive, a move seen as a bid to overcome a potential loss in Ohio. No Republican has ever captured the White House without carrying Ohio.