After the short-lived euphoria of his re-election, President Barack Obama immediately set about the daunting task of ending the partisan gridlock of a bitterly divided US Congress..

Before leaving Chicago and returning to the White House Wednesday, Obama was already on the phone trying to bridge the gap with Republican leaders to avoid a catastrophic "fiscal cliff" that could plunge the fragile American economy back into recession.

A combination of dramatic spending cuts and tax increases will take effect on January 1 without a deal on reducing the ballooning budget deficit, with Democrats and Republicans in Congress locked in a who-blinks-first stand-off.

Obama called congressional leaders, sending out an overt message that his priority was to try to break the deadlock in the lame-duck session of Congress that precedes his January 21 inauguration ceremony.

He spoke to Republican House Speaker John Boehner and also telephoned the minority Republican leader in the Senate, Mitch McConnell, as well as top Democrats.

"The president reiterated his commitment to finding bipartisan solutions to reduce our deficit in a balanced way, cut taxes for middle class families and small businesses and create jobs," a White House official said.

Obama believes that by returning him to the Oval Office, American voters signaled to Washington that both parties must set aside partisan interests and put the economy first, the official said.

But Boehner offered little during a Wednesday press conference in which his opening gambit was an unpalatable short-term fix to the "fiscal cliff" that the president has repeatedly opposed.

Obama arrived back at the White House at 2355 GMT following his unexpectedly decisive victory, claiming almost all the states he won in his historic 2008 electoral college landslide.

A campaign official said on the flight that election night returns unfolded very close to what the Obama team had expected though there was surprise at how quickly US television networks called the race.

Key to victory was the "ground game" waged in battleground states.

In explaining the superiority of Obama's operation, the official mentioned a conversation he had with a top field director on Monday, in which he said a rival Republican had tweeted that Romney's team had knocked on 75,000 doors in the must-win state of Ohio the previous day.

Not to worry, the director said, "we knocked on 376,000."

Obama triumphed despite the highest unemployment rate of any US president since Franklin Roosevelt in 1936 and became only the second Democrat since then to win a second term -- the other being his stalwart supporter Bill Clinton.

With Florida still totaling up the last remaining ballots after another embarrassing vote-counting debacle in the "Sunshine State," Obama had 303 electoral college votes, easily surpassing the 270 needed to win.

In a soaring victory speech, the 51-year-old president sought to revive the great hopes he stirred in 2008, promising "the best is yet to come" and hinting at a far-reaching agenda in his second term.

But his in-tray is already overflowing with first-term plans thwarted by blanket Republican opposition, whether it be comprehensive immigration reform, education, or a grand plan to rein in the troublesome deficit.

The big question for Obama is this: Will the Republicans be willing or can they be pressured to strike a meaningful deal that will avoid the prospect of a disastrous economic crunch forced by mandatory budget cuts?

"In the weeks ahead, I also look forward to sitting down with Governor Romney to talk about where we can work together to move this country forward," the president told the country in his rousing acceptance speech.

But Obama knows it is not his vanquished foe that he must now deal with but rather the Republican leadership in Congress, which may dig its heels in after failing in its stated goal: to make him a one-term president.

As Obama's victory was confirmed with wins in Ohio and Iowa, large crowds assembled outside the White House, chanting "four more years" and "O-bama, O-bama."

Republican nominee Romney, 65, deflated and exhausted, offered a dignified tribute, as he consoled dejected supporters in Boston moments after phoning Obama to formally concede.

"This is a time of great challenges for America and I pray that the president will be successful in guiding our nation," Romney said.

Obama's victory means he will get the chance to embed his healthcare and Wall Street reforms deep into the fabric of American life. Romney had pledged one of his first acts would be to repeal Obamacare.

The president may also be able to reshape the Supreme Court in his liberal image for a generation, a move that could shape policy on abortion and gay rights.

Obama will also face a challenge early in 2013 over whether to use military force to thwart Iran's nuclear program.

The president ran for re-election on a platform of offering a "fair shot" to the middle class, of fulfilling his pledge to end the war in Iraq, killing Osama bin Laden, and starting to build a clean energy economy.

But Obama also ran a fiercely negative campaign branding Romney -- a multi-millionaire former corporate turnaround wizard and ex-governor of Massachusetts -- as indifferent to the woes of ordinary Americans.

Remarkably, Obama's coalition of Hispanic, black, and young voters turned out in similar numbers to those of his heady change-fueled campaign in 2008, shocking Romney's team and presenting a new American face to the world.

In what is likely to be Obama's first foreign trip since re-election, a Myanmar government official announced that the US president would visit the former pariah state on November 19.

Democrats kept the Senate in Tuesday's vote but fell short of the 60-vote super-majority needed to sidestep Republican blocking tactics.

And on a night that saw liberal-championed measures on same-sex marriage and legalizing marijuana approved in several states, the Democrats also clawed back a couple of seats in the House but the Republicans retained control.