Donald Trump's jaw-dropping White House win is a slap in the face for Barack Obama, elected eight years ago as the country's first black president on the promise of a nation united.

At the political level, Hillary Clinton's defeat is certainly a setback for Obama, who campaigned hard for his former secretary of state, travelling across the country and employing the charisma and charm that she sorely lacks.

But, aside from being the loss of a typical battle between the two major American political parties, the 70-year-old real estate tycoon's success is also a stinging personal blow for Obama.

It certainly appears that as if this ever calm, cerebral and optimistic president failed to understand a large slice of the American electorate and appreciate their reflexes, fears and concerns.

Indeed, it would seem Obama has failed to take the pulse of this other America, a world of working class whites who felt they have been left in the lurch amid rapid fire change from globalisation and an increasingly multicultural society.

Over the short term, Obama, whose approval ratings remain high as he prepares to leave office in January, might well ask what will even be left of his legacy after a Trump administration.

Trump has promised to scrap or overhaul many of Obama's signature initiatives, such as the health care plan that bears his name, the battle against climate change and the Paris accord of 2015, and the proposed Trans-Pacific Partnership trade deal.

Obama has stated adamantly that Trump, criticised as a loose gun on everything from foreign policy to his treatment of women, is a danger to democracy.

"We can't afford the other guy. Can't do that! Can't do that!" Obama said in Las Vegas a few days ago.

Tolerance on the ballot

At the political and human levels, it is hard to imagine two people more different than Obama and Trump.

This means their world view but also their views on women ─ Trump was accused during the campaign of sexual misconduct ─ family, money and institutions, and even their style, the way they speak and the words they use.

Obama, the son of a Kenyan father and an American mother, forged a path that led him to Harvard and Yale. Trump inherited money from his family and developed a real estate empire centred on hotels and casinos.

He has boasted about paying as little as possible in taxes.

Obama is an intellectual who likes intricately reasoned discourse, at times to a fault. Trump is a businessman who speaks his mind in blasts of short, aggressive and sometimes vulgar phrases.

"Democracy itself" is at stake in the election, Obama said recently as he lashed out at Trump. "Civility is on the ballot," Obama added. "Tolerance is on the ballot. Courtesy is on the ballot. Honesty is on the ballot. Equality is on the ballot. Kindness is on the ballot."

Obama had personal reasons to try to stop Trump.

In 2011, Trump was not yet a candidate for the White House but had displayed a taste for the limelight, controversy and conspiracy theories.

For months, he fuelled the so-called "birther" movement that questioned whether Obama had been born on US soil and was thus eligible to be president.

An exasperated Obama called this nonsense and held a press conference to show off his birth certificate.

He was born in Hawaii.

A few days later, at the White House Correspondents Dinner, attended by Trump, Obama cheerfully said what he thought of Trump.

"No one is happier, no one is prouder to put this birth certificate matter to rest than the Donald," Obama said.

"And that's because he can finally get back to focusing on the issues that matter ─ like, did we fake the moon landing?"

Just over five years later, Obama is getting ready to give up the White House to his former foil.