White House 2024: The hopefuls aiming to take on Biden

As US President Joe Biden bids for a second term, a cast of characters that looks at once novel and familiar has lined up to stand in his way.

Among the declared and prospective 2024 candidates are Biden's old adversary Donald Trump, a hard-line conservative state governor, a former diplomat and a member of the Kennedy clan who has turned his back on the Democrats.

Donald Trump 

Is the United States about to witness a rerun of the 2020 election?

Despite his historic indictments -- or perhaps because of them -- former president Trump is soaring ahead of the pack in his bid for the Republican Party's nomination, making a rematch against Biden the most likely outcome.

Trump, 77, shocked the country and the world with one of the most unlikely political victories in US history when took the Oval Office in 2016.

Since then dogged by investigations into his finances, his efforts to overturn the 2020 election and his hoarding of government documents, Trump has been reprising his complaints of a "witch hunt" by a liberal cabal of "deep state" conspiracists while on the 2024 campaign trail.

Ron DeSantis

Many Republicans who are not all-in on Trump have been pinning their hopes on the candidacy of Ron DeSantis -- who, at the age of 45, was once seen as a rising star of the right.

But his campaign has failed to gain traction and the Florida governor has been going backwards in his bid to close a massive gap on Trump.

The former US Navy officer was narrowly elected to lead the Sunshine State in 2018 after securing an endorsement from Trump, whose ideas he shares -- if not the propensity for scandal.

DeSantis has distanced himself from his erstwhile mentor while doubling down on Trump's populist "America First" agenda, railing against "woke" indoctrination in public institutions and taking a hard line on immigration.

Nikki Haley 

A former governor of South Carolina and Trump's first ambassador to the United Nations, Nikki Haley is the only woman in the Republican primary contest.

Casting herself as a perennially underestimated underdog who has never lost an election, the 51-year-old daughter of Indian immigrants has spoken proudly of her time in the Trump administration.

But she has criticized her former boss's post-election crusade to relitigate debunked claims of voter fraud that he falsely alleges cost him the 2020 election.

She is still a long way behind but has seen her numbers surge in the all-important first nominating state of Iowa, where she is now tied in second with DeSantis.

Vivek Ramaswamy 

Fast-talking newcomer Vivek Ramaswamy emerged from the first Republican debate as the most talked about candidate, and hopes his provocative rhetoric will propel him all the way to the White House.

But the 38-year-old entrepreneur hasn't made any friends among his more experienced rivals, declaring at the event in Milwaukee that he was "the only person on stage who is not bought and paid for."

Ramaswamy calls environmental activism a "religious cult," has claimed the "truth about 9/11" is still unknown and often denies having said things that he is on the record as having said.

A political novice, he likes to think of himself as Trump 2.0, and has risen to fourth place in the polls for the Republican primaries, which begin in early 2024.

The rest 

It seems a matter of when, not if, they drop out for South Carolina Senator Tim Scott, North Dakota Governor Doug Burgum and former Arkansas governor Asa Hutchinson, who have failed to make a dent in Trump's lead.

Trump's biggest antagonist, former New Jersey governor Chris Christie, is polling marginally ahead of that trio but still has no credible path to the Oval Office.

But while the race for the Republican nomination may end up being the only show in town, two Biden challengers have emerged from the Democratic camp.

Best-selling author Marianne Williamson has not troubled Biden at all in the Democratic primary, where she was competing with Robert F Kennedy Jr. for a distant second place finish.

But the conspiracy theorist scion of the political dynasty that produced JFK has scrapped his primary challenge, launching a third-party bid in the election proper as an independent.

Kennedy's stance against the Covid-19 vaccine has won him admirers on the far right, and early polling suggests he may be more of a threat to Trump than to Biden.