In his acceptance speech, President Obama promised an electrified crowd in Chicago, Ill., that he would "work with leaders of both parties to meet the challenges" Americans face.

Updated at 4:02 a.m. ET: President Barack Obama won four more years in office on Tuesday, describing his victory over Republican nominee Mitt Romney as a call to action that would help move the U.S. past the difficult times endured during the past four years and promising "the best is yet to come."

Propelled by wins in Ohio, Wisconsin and Iowa – states long touted as Obama’s “firewall” insulating him from his GOP challenger – the president won a long-fought election in which the economy, its slow pace of recovery and Obama’s management of it, became the central issue.

Emerging early in the hours on Wednesday in Chicago to the tune of Stevie Wonder’s “Signed, Sealed, Delivered, I’m Yours” the president struck an upbeat note about the challenges that lie ahead during a second term, with which he’ll have to reckon almost immediately in the next few weeks.

President Obama addressed an exuberant crowd, saying he's "never been more hopeful about America" and suggesting the country is not as divided as its politics might suggest.

“A decade of war is ending. A long campaign is now over. And whether I earned your vote or not, I have listened to you, I have learned from you, and you have made me a better president,” Obama said. “With your stories and your struggles, I return to the White House more determined and more inspired than ever about the work there is to do and the future that lies ahead.”

But there were strong indications that the first two years of Obama’s second term would resemble the final two years of his first term – that is with a Republican-held House and nominally Democratic Senate stalemated over major tax and spending issues, as the balance of power in Congress remained unchanged after Election Day.

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The specter of gridlock appeared quickly as Obama prepared to confront the immediate task in addressing the series of automatic tax hikes and spending cuts – the so-called “fiscal cliff” – set to spring into place at the end of this year.

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As Obama won a second term, House Speaker John Boehner, R-Ohio, said Republicans’ retention of their House majority meant “the American people have also made clear that there is NO mandate for raising tax rates.” And Senate Minority Leader Mitch McConnell was even tougher in his statement, saying, “The voters have not endorsed the failures or excesses of the president’s first term, they have simply given him more time to finish the job they asked him to do together with a Congress that restored balance to Washington after two years of one-party control.”

President Barack Obama gives a victory speech Tuesday after being elected to a second term in the White House.

Obama nodded to the challenges that lay ahead in his Tuesday evening speech, hinting that he wishes to meet with Romney – as the president had done with Arizona Sen. John McCain after the 2008 election – to seek his help in moving past some of the most intractable problems to beguile Washington.

“Tonight, despite all the hardship that we’ve been through, despite all the frustrations of Washington, I have never been more hopeful about our future,” Obama told a boisterous crowd in his adoptive hometown of Chicago.

In addition to the looming fiscal cliff, Obama will also have to confront a reshuffling of his cabinet. Both Secretary of State Hillary Clinton and Treasury Secretary Timothy Geithner have suggested that they might depart the administration after Obama’s first term, setting up a major remaking of Obama’s inner circle.

Slideshow: Election 2012 Kevin Lamarque / Reuters Campaigning with Mitt Romney and Barack Obama, voting and election results. Launch slideshow

After months of campaigning that saw ad spending alone reach the $1 billion mark, Obama won a second term with much of his 2008 electoral map intact. Romney managed to flip only North Carolina and Indiana, which Obama won four years ago, back to Republicans in 2012; the GOP nominee failed to put into play more traditionally Democratic states like Wisconsin and Pennsylvania, on which his campaign concentrated its efforts in the closing weeks of the campaign.

The Midwestern troika of Ohio, Iowa and Wisconsin helped insulate the Obama campaign from Romney and preserve Democratic inroads in other states, like Colorado and Virginia.

'We have given our all'

After having claimed momentum in the final days of the campaign, the erstwhile GOP nominee emerged in Boston shortly after 1 a.m. ET to offer his concession, a conciliatory speech capping a bid for the presidency for Romney that has spanned the better part of a decade.

"This is a time for great challenges for America, and I pray that the president will be successful in guiding our nation," the former Republican nominee said, joined by his running mate, Wisconsin Rep. Paul Ryan (who won re-election to Congress) and their families.

GOP presidential nominee Mitt Romney gives his concession speech Tuesday after President Barack Obama was declared the winner of the 2012 presidential race.

"Like so many of you, Paul and I have left everything on the field. We have given our all to this campaign," Romney said. "I so wish that I had been able to fulfill your hopes to lead this country in a different direction, but the nation chose another leader."

While Romney had campaigned on his own private sector expertise amid a weak economic recovery, improvements in hiring and confidence in the economy allowed Obama to parry his opponent’s criticism.

Exit polls suggested that the economy was, by far and away, the issue at the front of voters’ minds on Election Day. Romney edged Obama nationally by six points among voters who said the economy was their top issue.

Obama outperformed Romney on questions of empathy, and voters nationwide were virtually tied on the more direct question of who would better handle the economy and the budget deficit.

Obama also held a demographic edge over Romney among two key groups of voters. The president bested the former Massachusetts governor by 10 points among women (Romney beat Obama by 8 percent among men). Hispanic or Latino voters also broke heavily for Obama by a 39-point margin.

But despite lingering divisions, the president emphasized points of unity, Wednesday morning, saying the nation “moves forward because you reaffirmed the spirit that has triumphed over war and depression, the spirit that has lifted this country from the depths of despair to the great heights of hope, the belief that while each of us will pursue our own individual dreams, we are an American family, and we rise or fall together as one nation and as one people.”

Watch the drama of election night quickly unfold in a three minutes montage of sights and sounds.

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