He has suffered profound personal tragedy and seen his earlier political ambitions thwarted, but veteran Democrat Joe Biden hopes his pledge to unify Americans will deliver him the presidency after nearly half a century in Washington.

Rarely has the profile of opposing presidential nominees differed so sharply as in the 2020 race, which pits the empathetic Biden, with decades of leadership and a blue-collar upbringing, against brawling President Donald Trump, the billionaire businessman who insists he remains the outsider.

But in his decades-long White House quest -- Biden has run twice before -- the optimist from Delaware maintains he can shift the tone in America from anger and suspicion to dignity and respect.

At 77 and leading in the polls just days ahead of the November 3 vote, Biden is on the cusp of becoming America's oldest ever president.

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

But just 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 in 2015. The tragedies help nourish the empathy that shines through in Biden's interactions with everyday Americans.

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.

However, opponents, and even some Democrats, wondered whether Biden, garrulous and gaffe-prone, would stumble in his long campaign against Trump. Trump regularly calls him "Sleepy Joe" and accuses him of diminished mental acuity.

Elected one of the youngest senators ever, he spent more than three decades in the upper chamber before serving eight years a Barack Obama's deputy.

He offers moderate politics in a divisive time, but he has pledged to take progressive action as president, on climate change, racial injustice and student debt relief.

Biden almost did not make it this far. Despite being the favorite of the Democratic establishment, he was deemed by some to be too old or too centrist.

His campaign looked like it was 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 plagiarizing a speech by British politician Neil Kinnock.

In 2008 he hardly fared better, dropping out after mustering less than one percent of the vote in Iowa's caucuses. That year he was ultimately picked as running mate by Obama. After their victory Obama quickly assigned Biden to oversee the economic recovery during the last recession.

He faced a reckoning among Democrats for associating with known segregationists in the Senate and, in the midst of 1970s desegregation, for opposing "busing" policies 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.

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

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 neighboring Delaware when Joe Biden was 10.

Biden, a devout catholic, studied at the University of Delaware and the Syracuse University law school. He touts his working-class roots and recalls being hampered as a child by a stutter so bad he was cruelly nicknamed "Dash."