Though it became clear last night that the President would secure a significant victory in the Electoral College, as Mr Obama addressed the Chicago rally at 12.50am local time it was also clear the nation remains deeply divided, with counting showing he had won just 50 per cent to Mitt Romney's 48 per cent.

Both men addressed the disunity in their speeches. 

Obama's disciplined, ruthless campaign

Why Romney lost the US election

The President told his celebrating supporters: "Our economy is recovering. 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 learnt from you, and you've made me a better President."

Harking back to his famous convention speech of 2004, he said: "Believe we can seize this future together because we are not as divided as our politics suggests. We're not as cynical as the pundits believe. We are greater than the sum of our individual ambitions, and we remain more than a collection of red states and blue states. We are and forever will be the United States of America."

He said the campaign had been fought so hard not because of division but because people passionately believed in the country.

An hour earlier, conceding defeat in Boston, Mr Romney said: "The nation, as you know, is at a critical point. At a time like this, we can't risk partisan bickering and political posturing.

"Our leaders have to reach across the aisle to do the people's work. And we citizens also have to rise to the occasion."

After the bitter $2 billion campaign the balance of power remains exactly as it was in the previous gridlocked term – with Democrats holding the White House and the Senate and Republicans holding the House of Representatives.

The President must now begin negotiations with the Republican House Majority leader, John Boehner, to avert the "fiscal cliff" – a set of automatic spending cuts and tax rises set to kick in on January 1 that were agreed when the two parties failed to negotiate a budget.

The impact could return America to recession if it is not avoided, though it is expected both parties will agree to shift the deadline if they fail to come to an immediate solution.

Last night Mr Boehner issued a statement declaring both parties had won a mandate, suggesting those negotiations may continue to be fraught.

With the Republicans drawn to a coalition of conservative and Christian Evangelical voters by the Tea Party, Mr Obama sought and won 80 per cent of the minority vote and 40 per cent of the white vote. He led among women and young people, too.

Early exit polls showed 28 per cent of the vote was non-white and of that group the President won 91 per cent of the African American vote and 72 per cent of Hispanics, while Mr Romney won 60 per cent of white voters.

Mr Obama campaigned on immigration reform and Democrats attacked Republicans over opposition to abortion rights and plans to cut funding to Planned Parenthood.

The President repealed the Don't Ask, Don't Tell law, voiced his support for gay marriage and passed equal pay legislation.

Some early exit data suggested Mr Obama won among women – who constitute 53 per cent of the vote – by 10 points. At least 18 women will serve in the new Senate, a record.

The failure of the Republican Party to recognise and embrace America’s changing demographics became a heated topic early in the evening on Fox News. Commentator Bill O’Reilly declared the ‘‘white establishment’’ had lost its dominance.

‘‘The white establishment is now the minority,’’ he said.

‘‘And the voters, many of them, feel that the economic system is stacked against them and they want stuff. You are going to see a tremendous Hispanic vote for President Obama, overwhelming black vote for President Obama, and women will probably break President Obama’s way. People feel that they are entitled to things and which candidate, between the two, is going to give them things?’’

‘‘The demographics are changing,’’ he said. ‘‘It’s not a traditional America anymore.’’ 

A short time later former governor Mike Huckabee – himself a prominent conservative commentator – said on the same program, ‘‘I think Republicans have done a pathetic job of reaching out to people of colour.’’

The share of white voters has shrunk in every election since 1992, from 87 per cent to 74 per cent in 2008.

The Tea Party Senate candidate Richard Mourdock – who caused controversy during the campaign for saying that if a woman was raped and became pregnant, that was ‘‘something that God intended to happen’’ – lost a formerly safe Republican seat.

Todd Akin, who said women who suffered ‘‘legitimate rape’’ could not get pregnant, lost his race against the Democratic incumbent Claire McCaskill. 

Michele Bachmann, another Tea Party star, was fighting to keep her seat.   

The President’s campaign was ruthless and disciplined. The moment Mr Romney became the Republican candidate Mr Obama’s Chicago campaign headquarters unleashed a torrent of negative advertising, first casting him as a plutocrat who stashed funds in offshore accounts, then as a corporate raider who had built his fortune by flipping companies and offshoring jobs.

Unable to campaign on his record as governor of Massachusetts because he had supported healthcare reforms similar to the President’s, it seemed for a time Mr Romney would be unable to boast about his remarkable record as a businessman.

Only when he demolished the President in the first debate did things turn around for him. The arch conservative who had campaigned on the right to win his base suddenly turned into moderate Mitt, and rather than being punished for it he jumped ahead in the polls for the first time.

But the Obama campaign stuck to the strategy constructed by Jim Messina, and with the President’s better performances in the remaining two debates, plus its vast volunteer army, it erased the Republican lead.

The  failure to topple a president who was perceived as weak and divisive is expected to provoke a bloodletting in the party.