Barack Obama's re-election for another term in the White House opens a new chapter in the already historic tale of the first black president of a nation scarred at birth by a deep racial fault line.

But for Obama partisans his re-election was essential. Only with a full eight years at the helm of the US presidency will he be remembered for the change he wrought and not just for the change he represented.

Though it was key to the euphoria that greeted his first election in 2008, Obama's race has rarely been a dominant political theme since.

Quickly, the same political dynamics faced by many of his predecessors: divided, vicious, partisan politics threatened to swamp the 44th US president.

All presidents crave the validation of a second term but for Obama that desire may have been even more keen, as his Republican foe Mitt Romney had vowed to quickly reverse much of his legacy.

Obama's whole political project, the idea that America is not as divided as it seems, that a grass roots movement can change a nation from the bottom up, and that hope has tangible political power, was on the line.

"Our destiny is not written for us; it's written by us," Obama told a crowd at a recent New Hampshire rally, seeking to revive the sense of possibility that powered his first election win, but has since dissolved.

"We look forward to that distant horizon, to that new frontier. We imagine a better America and then we work hard to make it happen."

Now, much of Obama's second term will be devoted to cementing the legacy of his first.

He will enshrine his health care reform -- the most sweeping social legislation for 50 years, which Romney promises to end on his first day in the Oval Office -- deep into American life.

Obama may get several more chances to reshape the Supreme Court for a generation, after adding two women, including the first Hispanic justice in his first term.

And the president, 51, will solidify his reforms on gay rights, women's rights, student loans and financial reform and may yet even seek ways to tackle global warming and immigration reform.

Obama, now a graying, sometimes terse and wizened figure is a changed man from the beaming young dreamer who bounced onstage in early 2007, on a bitterly chill day in Illinois, and announced his presidential bid.

"You have seen the scars on me to prove it. You've seen the gray hair on my head to show you what it means for fight for change, and you have been there with me," he told a crowd on Monday in Madison, Wisconsin.

Rocketing from political obscurity, Obama, a senator for only two years, promised to use "the power of hope" to transform a nation -- a message he belted out to massive 2008 crowds, often moving his audience to tears.

He invoked a politics where people could "disagree without being disagreeable."

But the hope and optimism of his win over Republican John McCain barely survived the first contact with polarized Washington politics.

Obama the president emerged as an elusive figure of many contradictions.

A Nobel Peace laureate who got US troops out of Iraq, Obama ruthlessly applied lethal force in a drone war and the mission to kill Osama bin Laden.

Candidate Obama chided political leaders who feuded over "small things" yet lambasted his 2012 foe for a flip flopping condition he calls "Romnesia."

Obama inspired a generation to get into politics for the first time: but once president, appeared to disdain the grubby business of getting things done in Washington.

He was devoted to the grand gesture on the world stage -- for example his speech to the Muslim world in Cairo in 2009 -- but despite some success, his presidency hardly transformed America's place in the world.

And the hope that exploded in 2008 soon fizzled.

Four years on, Obama is locked in a grim grind to the finish with the joy of four years ago but a memory.

Some things have not changed. Obama retains the burning self confidence, -- foes call it arrogance -- and a fierce will to win.

In its way, victory on Tuesday night could be historic in its own right, as Obama defied a level of economic blight that made other presidents one termers.

Busting convention is written in Obama's political DNA -- not for him a political apprenticeship in the Senate: he left to slay the mighty Hillary Clinton machine in the 2008 Democratic primary.

Matching dazzling oratory with a formidable grass roots network, Obama, along with cerebral aides like David Plouffe, re-invented how US elections are won in 2008.

His massive operation will redefine re-election races if he wins next week.

Obama, despite the claims of conservative conspiracy theorists, was born in Hawaii in 1961 to a black Kenyan father and white mother from Kansas. His father abandoned the family when "Barry" Obama was just two.

His mother Ann, an anthropologist who died in 1995, took her son with his new stepfather to Indonesia and he returned to live with his grandparents in Hawaii in his restless teens.

After attending an elite Hawaii academy and two colleges including Columbia University in New York, Obama went to the elite Harvard Law School and was the first African-American to edit the Harvard Law Review.

Married in 1992 to Michelle, a fellow lawyer, Obama rose through bare-knuckle world of Illinois politics then announced himself to the world at the 2004 Democratic convention.