Elsewhere in the city, GOP poll monitors were being escorted into precincts by sheriff's deputies after some observers had been denied access earlier in the day, said Tasha Jamerson, a spokeswoman for the district attorney's office.

In New Jersey, which permitted electronic balloting in the aftermath of last week's storm, the state chapter of the American Civil Liberties Union headed to court on Tuesday on behalf of voters who said their requests for an electronic ballot weren't being acknowledged.

Candidates usually take Election Day off, but both sides made public appearances even as voting was under way.

Obama visited a local Democratic election center in the Chicago area, while Vice President Joe Biden made "an unannounced but long-scheduled" stop in the key battleground state of Ohio.

Romney and his running mate, Rep. Paul Ryan, also arrived separately in Ohio, with Romney's campaign plane and Air Force Two, which carries the vice president, crossing paths at Cleveland's airport.

Only a handful of states were considered up for grabs and both candidates and their campaigns concluded an exhausting final sprint through them over the weekend and on Monday.

The barnstorming amounted to a montage of Americana electioneering, with Obama and Romney shouting themselves hoarse before boisterous crowds, joined by top surrogates and star power such as Bruce Springsteen singing for Obama and Kid Rock for Romney.

Emotion overtook the president at the end of the day.

His eyes welled with tears as he thanked the people "who've given so much to this campaign over the years," during a stop in Des Moines, Iowa -- a place where his first campaign gained an early foothold in his first run for the White House.

"You took this campaign and made it of your own and you organized yourselves block by block, neighborhood by neighborhood, county by county, starting a movement that spread across the country," Obama said wiping away tears as he talked.

For his part, Romney called Obama's record one of underachievement and failure, telling a cheering Virginia crowd at his second stop of the day that "almost every measure he took hurt the economy, hurt fellow Americans."

For Romney, a multimillionaire businessman seeking to become the nation's first Mormon president, the election concluded a six-year quest for the presidency.

Romney also failed in his first bid for the Republican nomination in 2008, then spent the next two years preparing for a second run that began in 2011 with a grueling primary campaign featuring a record 20 debates.

Romney, 65, shifted to the right for the primary race to overcome a broad field that included former House Speaker Newt Gingrich, former Pennsylvania Sen. Rick Santorum, Rep. Michele Bachmann of Minnesota, Texas Gov. Rick Perry, former U.S. Ambassador to China Jon Huntsman and businessman Herman Cain.

Romney declared himself "severely" conservative and adopted stances against abortion, gay marriage and a path to legal residency for undocumented immigrants while also opposing higher tax rates as part of a deficit reduction plan. His support remained steady -- though well below a majority -- throughout the primary campaign while opponents dropped out one by one until Romney emerged as the winner and claimed the nomination at the GOP convention in late August.

However, his campaign endured a tough September, due in part to some unforced errors. A secretly recorded video from a May fundraiser became public, showing Romney referring to 47% of the country as dependent on government handouts and therefore unreachable to him as a candidate.

When U.S. diplomatic compounds came under attack on September 11, including an assault that killed the U.S. ambassador and three other Americans in Benghazi, Libya, Romney quickly issued a statement that was criticized for mistaken information and seeking to politicize a sensitive national security issue.

In the first presidential debate on October 3, Romney began an energetic shift back to the political center and scored a clear victory over Obama by presenting himself as more moderate than the right-wing zealot portrayed by the president.

Obama's lackluster showing in the first debate contributed to an overwhelming consensus among analysts and poll results that Romney carried the night. He began rising in the polls to erase what had been a consistent Obama lead since the conventions a month earlier.

Stronger performances by Obama in the second and third debates slowed Romney's momentum.