Barack Obama was gaining crucial lastminute momentum towards a second presidential term on Monday night, as polls showed him emerging as a narrow but clear favourite when America votes on Tuesday in one of the bitterest and closest-fought elections in recent memory.
However, with the result likely to be decided by voters in just a handful of key battleground states, both sides were martialing teams of lawyers to contest an election that could still prove too close to call.
Even before polls opened, legal skirmishes were breaking out in Ohio and Florida as both sides argued over voter identification laws, raising the spectre of the protracted legal battles that followed the 2000 election.
As Obama and his opponent Mitt Romney made their final pitches to the voters in a series of rallies across the country yesterday, the two men were still effectively tied in polls of likely national voters, with Mr Obama holding just a 0.4-point lead on average, according to RealClearPolitics.
The president has retained his persistent and solid advantage in the race to win the 270 Electoral College votes that will secure the White House, thanks to his leads in polls from the battleground states of Iowa, Nevada, New Hampshire, Ohio and Wisconsin.
Of the 12 states that are closest to call, Romney was ahead in only two last night - Florida, where he spent the morning rallying supporters, and North Carolina, a usually solid Republican state that Obama won by just 14,000 votes in 2008.
"I predict it will not be tied tomorrow, we're going to win," said David Axelrod, Obama's chief campaign strategist, reflecting growing Democrat confidence that the race was now firmly within their grasp.
But in a sign of how tight the race might still be, lawyers were already wrangling over 2,00,000 potential provisional votes in Ohio after the state's Republican secretary of state issued an 11th hour directive saying any ballots that did not include social security numbers would be invalidated.
The move was seen as direct attempt to target Democrat voters - who tend to vote early and are less likely to have correct documentation - and caused Ohio's Democratic leadership to issue a statement promising the move would be met with "overwhelming legal force".
Elsewhere, in New Hampshire, there were reports of absentee ballots failing to arrive with voters, while in Iowa some received them despite not requesting them. In New York an official suggested there could be an extra day of voting if counties affected by Superstorm Sandy had turnout of less than 25%.
"Provisional ballots could very likely be the hanging chads of 2012. The battle over provisional ballots will take centre stage where any election is close and a significant number of such ballots have been cast," said Jocelyn Benson, law professor at Wayne State University in Detroit.
Democrats strategists, however, were showing increasing signs of confidence that the outcome of the race would not be close enough to be materially affected by many of these challenges.
David Plouffe, the Obama campaign turnout guru, said the infrastructure in place to grind out a win today was "light years ahead" of the much-vaunted 2008 campaign. This election has laid bare deep divisions in the US, pitting Romney's conservative coalition of overwhelmingly older, male, white, rural Christian voters against Obama's younger, urban liberal votebank of ethnic minorities, the college-educated and women.
On Monday, both men advanced their arguments one final time, Romney swinging through four battleground states making a final plea to voters to help him restore the small-government, low-taxation and entrepreneurial spirit that made America. Romney's aides insisted that he would defy the forecasts of the majority of major pollsters.
Meanwhile, Obama, was in Madison, Wisconsin, revving up a huge crowd with the help of Bruce Springsteen, the singer. For much of this campaign even Obama's supporters have complained that their candidate has seemed withdrawn, but yesterday it was the Barack Obama of 2008 that reported for duty.
"Are you fired up?" he asked the crowd, "Are you ready to go?" he added huskily, and 18,000 people roared back their reply with the kind of enthusiasm Democrats say will win them the vote.
Obama has ended the race promising to be a "champion" for America's middle classes, contrasting his "fair-shake" agenda with Romney who he accused of repackaging the Bush-era economic policies that helped cause the 2008 financial crisis.
Aides were bullish on Mondau night announcing that Obama would play his regular game of "pick up" basketball with friends in Chicago today, in an effort to show him as relaxed as possible.