He has channeled personal tragedy into a heart-on-his-sleeve compassion for everyday Americans, but US President-elect Joe Biden faces the challenge of a lifetime as he inherits a nation both traumatised and spellbound by his White House predecessor.

Biden's victory — projected by TV networks on Saturday in a cliffhanger election with the United States in crisis — turns the page on Donald Trump's most divisive of presidencies, and rewards his appeal to the better angels of a deeply-riven country.

But can the man who has cast himself as healer-in-chief make headway in a nation where Trump's ideology, regardless of the president's defeat, shows little sign of diminishing? Rarely have presidential rivals differed so sharply as in the 2020 race, which pitted the empathetic Democrat against the brawling Trump, the billionaire businessman who ran as the outsider despite his four years in the Oval Office.

As the sun rose on Washington's National Mall, the morning after a fraught Election Night, the razor-tight contest looked as if it could go either way.

But as the quietly confident Democrat picked up state after state in the ensuing days, his victory slowly but inexorably took shape.

By Saturday, US networks projected he won the pivotal state of Pennsylvania — and the White House. “The work ahead of us will be hard, but I promise you this: I will be a President for all Americans,” the 46th US president-in-waiting said shortly after networks made the call.

Now, all of his work is ahead of him.

He inherits a coronavirus pandemic that shows no signs of abating and an office he believes has had its credibility shattered by the “liar” Trump.

Biden ran for the White House twice before, in 1987 and 2008.

A loss to the deeply polarising Trump, Biden said in the election's final stretch, would mean he had been a “lousy” candidate, lowering the curtain on a prolific but ultimately unfulfilled political career.

But “Middle Class Joe” had made it his life's crowning mission to unseat the Republican and, in his words, restore the “soul” of America.

And despite a campaign muted beyond recognition by Covid-19 — conducted largely from home while his high-octane rival charged around the country — Biden ultimately showed Trump the door.

Enduring compassion

When he takes the oath of office on January 20, at age 78, Biden will be the oldest US head of state ever inaugurated.

He hit the national stage at just 29, with a surprise US Senate win in Delaware in 1972.

One month later tragedy struck: his wife Neilia and their one-year-old daughter Naomi were killed in a car crash as they were Christmas shopping.

Biden's two sons were severely injured but survived, only for the eldest, Beau, to succumb to cancer four decades later, in 2015.

Throughout his life Biden has spoken poignantly of his personal encounters with tragedy, seen as having nourished a capacity for genuine empathy — something Trump failed to demonstrate even as the toll from Covid-19 climbed towards a quarter million.

His retail politicking skills are peerless: he can flash his million-watt smile at college students, commiserate with unemployed Rust Belt machinists, or deliver a fiery admonishment of rivals.

That personable, gregarious quality was curtailed by the pandemic, which brought in-person campaigning to a halt in March and prompted a more cautious Biden on the trail.

Somewhat diminished from the figure he presented during his eight years as Barack Obama's vice president, the dazzling smile remained. But Biden's gait was more delicate and his fine white hair had thinned.

Opponents, and even some Democrats, wondered whether Biden, garrulous and gaffe-prone, would stumble in his long campaign against Trump.

The 74-year-old president nicknamed him “Sleepy Joe” and accused him of diminished mental acuity. In a flash of frustration with Trump's interruptions during their first debate, he at one point told the president to “shut up”. But mostly Biden shrugged off the attacks.

'They are the future'

America's oldest president-elect started his Capitol Hill career as one of the youngest senators ever, and would spend more than three decades in the upper chamber before becoming Obama's deputy.

Biden's campaign message was built largely on his association with the still-popular Obama and on his ability to do business with the many world leaders his former boss sent him to meet (“I know these guys,” he would remind people).

His offer of moderate politics in a divisive time was a salve to an electorate exhausted by four years of scandal and chaos in the Trump White House.

But Biden balanced his mainstream appeal with a pledge to take genuinely progressive action as president, on climate change, racial injustice and student debt relief.

Come January, Americans may already be asking whether the elder statesman will seek to extend his role as US president beyond a first term, given his own words on the transitional nature of his candidacy.

“Look, I view myself as a bridge, not as anything else,” Biden told a crowd at a rally in Detroit, Michigan back in March.

He gestured to younger Democrats who had joined him on stage — including the woman who would become his running mate, 56-year-old Senator Kamala Harris.

“There's an entire generation of leaders you saw stand behind me,” he said. “They are the future of this country.”

Historic comeback

Biden was anything but assured of becoming his party's flagbearer. Despite being the favorite of the Democratic establishment, he was deemed by some too old or too centrist.

His campaign looked headed for disaster after disappointing primary losses to the fiery Bernie Sanders early this year.

But Biden came roaring back in South Carolina's primary on the strength of overwhelming backing from African-American voters, a crucial base of Democratic support.

Clinching the nomination marked a sharp contrast to his 1988 flameout, when he quit in disgrace after being caught plagiarising a speech by British politician Neil Kinnock.

In 2008 he hardly fared better, dropping out after mustering less than one per cent of the vote in Iowa's caucuses.

That year he was ultimately picked as running mate by Obama, who dubbed him “America's happy warrior”. As a senator for more than 30 years, Biden was known to forge unlikely alliances — and, like Trump, he developed a lack of fidelity to script.

He faced a reckoning among Democrats — including Harris, America's next vice president — for working with known segregationists in the Senate and for opposing “busing” policies in the 1970s aimed at transporting Black children to predominantly white schools.

He also caught flak for helping draft a 1994 crime bill which many Democrats believe drove up incarcerations, disproportionately affecting African Americans. Biden recently called the push a “mistake”.

Other Senate episodes also threatened to spoil his presidential campaign: his 2003 vote for the Iraq war, and his chairmanship of controversial hearings in 1991 in which Anita Hill accused Supreme Court nominee Clarence Thomas of sexual harassment.

Last year he faced a storm over his own notoriously tactile approach with female voters that could suggest a man out of step with his modernising party.

He apologised, and promised to be more “mindful” of women's personal space.

'Get back up'

Biden relays the heart-wrenching details of his family stories so often that, despite his obvious grief, they have become part of a political brand.

The 1972 accident left his sons Beau, four, and Hunter, two, badly injured, and the 30-year-old Biden was sworn in beside their hospital beds.

Biden met his second wife, teacher Jill Jacobs, in 1975 and they married two years later. They have a daughter, Ashley.

Both boys recovered from their injuries and Beau followed his father into politics, becoming attorney general of Delaware — but the Democratic rising star died of brain cancer in 2015 at age 46.

Lawyer and lobbyist Hunter Biden has had a different trajectory.

He received a lucrative salary serving on the board of a Ukrainian gas company accused of corruption while his father was vice president.

Trump's push for Ukraine to investigate the Bidens led to the president's impeachment last December by the Democratic-controlled House of Representatives, but he was acquitted by the Republican-led Senate.

Hunter was not personally accused of any criminal wrongdoing, but Trump wouldn't let the issue die. He repeatedly insisted the Bidens were a “crime family” getting rich off of corruption, but the accusations were of dubious origin and did not stick with American voters more concerned about bread and butter campaign issues, not to mention a once-in-a-lifetime public health crisis.

Joseph Robinette Biden Jr was born November 20, 1942 and raised in the Rust Belt town of Scranton, Pennsylvania, in an Irish-Catholic family.

His father was a car salesman, but when the city went through tough times in the 1950s and he lost his job, he moved the family to neighbouring Delaware when Joe Biden was 10.

“My dad always said, 'Champ, when you get knocked down, you get back up,'” Biden says.

He made Delaware his political domain. As a young man he served as a lifeguard in a majority-Black neighbourhood, an experience he said sharpened his awareness of systemic inequalities and strengthened his political interest.

Biden studied at the University of Delaware and the Syracuse University law school, and has expressed pride that he is not a product of the elite Ivy League.

He touts his working-class roots and recalls being hampered as a child by a stutter so bad he was cruelly nicknamed “Dash”. But he overcame the condition, and on the campaign trail spoke about how he still counsels youngsters who stutter.

Biden would often point to Jill, 69, as a powerful asset for his campaign, and recalled how she took over as mother to her husband's two boys.

“She put us back together,” Biden has said.

'Proud of me?'

“It never goes away,” Biden said of the pain that lives within him since losing Beau. The tragedy prevented him from launching a presidential bid in 2016.

Even today, he often stops to greet firefighters, recalling that it was they who saved his boys.

They saved Biden too. In 1988 firefighters rushed him to hospital after an aneurysm. Biden's condition was so dire that a priest was called to give him last rites.

Nearly every Sunday Biden prays at St. Joseph on the Brandywine, a Catholic church in his affluent Wilmington neighbourhood.

There in the cemetery rest his parents, his first wife and daughter — and his son Beau, under a tombstone decorated with small American flags.

In January, Biden confided about Beau and his undeniable influence: “Every morning I get up ... and I think to myself, 'Is he proud of me?'”