New York (AFP) - Bernie Sanders has emerged from the leftist hinterland of Democratic politics to become a frontrunner for the party's presidential nomination alongside moderate Pete Buttigieg.
AFP takes a look at the strengths and weaknesses of the 78-year-old former Vermont mayor who has the White House firmly back in his sights after falling short in 2016.
- Natural-born politician -
Despite being frequently written off by rivals and commentators, Sanders has proven time and time again that he is a well-organized, seasoned campaigner with a knack for winning.
He has been victorious in numerous contests for Senate, House of Representatives and mayoral seats, mostly as an independent, in a political career stretching back 40 years.
He's also lost his fair share but has used the bitter experience of defeat to improve as a candidate.
He relishes the cut and thrust of the campaign trail, delivering impassioned speeches railing against corrupt Wall Street elites that fire up crowds with talk of "political revolution."
Sanders knows the importance of bold, easily understood messages such as tax the rich, health care for all and free tuition and rarely ties himself in knots over the minutiae of policy.
- Ardent support -
Sanders has built up a huge grassroots following that remains steadfastly loyal to the man who pushed Hillary Clinton to the brink for the Democratic nomination in 2016.
Knocking on doors, attending his rallies in their thousands, and taking the fight to the opposition online, Sanders's followers are a young, committed bunch who rarely shy away from pushing his message.
Sanders's campaign has also been ignited by several celebrity endorsements, including from rising Democratic star Alexandria Ocasio-Cortez, rapper Cardi B and pop star Miley Cyrus, fueling an aura of youthful vitality around the septuagenarian.
- Flush with cash -
Sanders' campaign is not short of cash, with the senator from Vermont vastly out-fundraising his rivals in recent months.
A surge in donations has injected momentum into his run at a time when the likes of Massachusetts Senator Elizabeth Warren and early favorite Joe Biden have seen gifts to their cause start to dry up.
Sanders raised $34.6 million between October and December, according to the Federal Election Commission -- almost $10 million more than Buttigieg's $25.2 million.
Biden saw $23.3 million coming in while Warren banked $21.7 million.
Only billionaires Michael Bloomberg and Tom Steyer, who are largely backing themselves financially, are ahead of Sanders.
- Age and health -
Despite projecting a more youthful presence than Biden, who is a year younger, Sanders' status as the oldest candidate in the Democratic field will be seen as a weakness by some voters.
Born on September 8, 1941 in Brooklyn, New York, Sanders will be 79 by the time the US electorate heads to the polls on November 3.
If elected he would be the oldest US president to enter the White House, beating Donald Trump, who was 70 at the time of his inauguration, by almost a decade.
Sanders would be well into his 80s by the start of a second term. Buttigieg, on the other hand, is just 38 currently.
Sanders' age has raised fears about his health. He was forced to briefly suspend his campaign in November after suffering a heart attack, leading some commentators to speculate that his bid might be over.
- Narrow fan base -
While there is evidence that Sanders is picking up more support among ethnic minorities and women compared to his run four years ago, his supporters appear to be mainly young white men.
He will need to broaden his base to include more African-American and Hispanic supporters if he is to secure the Democratic nomination.
His standing among women voters may also negatively affect his chances. Warren and Clinton have denounced a toxic streak among Sanders' more ardent supporters, known as "Bernie Bros," accused of aggressive and at times sexist online tactics.
Sanders also forced to address stories that he told Warren that a woman could never win the White House -- a claim he denies making.
- Too left-wing? -
Sanders is a self-described "democratic socialist" in a country that prides itself on its foundational freedoms and thinks of socialism in some quarters as a dirty word.
Some Democrats worry that Trump, who routinely mocks Sanders as "Crazy Bernie," could successfully portray him as a dangerous communist in an election showdown.
He has also struggled to gain acceptance from the Democratic hierarchy -- not least because the he only registered with the party last year.
"He cannot win the nomination in a one-on-one contest against any moderate," said American University professor David Barker.