President Joe Biden is the latest candidate to enter the 2024 race for the White House and he could face a rematch against Donald Trump, after defeating him in 2020.
Mr Trump has already been out on the campaign trail after announcing his bid to return to the White House.
Should they both secure the nomination, it would be the first time since 1956 that two presidential candidates would face a rematch – but Mr Trump first has to emerge from a crowded Republican field.
The National takes a look at all the candidates running in 2024:
Democratic Party
Joe Biden: Despite his approval ratings hovering about 42 per cent, Mr Biden is all but assured to secure his party's nomination in 2024.
Mr Biden hinged his announcement on the phrase, “Let's finish the job”, contrasting his administration's policies with what he calls “Maga [Make America Great Again] extremists”.
As the incumbent, Mr Biden will have to defend his record as President and fend off criticism over his handling of the Afghanistan withdrawal, the US economy and his response to the war in Ukraine.
He has also used his position to lobby for stronger gun control policies and to preserve reproductive rights in the US.
Marianne Williamson: Self-help author Marianne Williamson has sought public office before, including a failed bid to win the Democratic nomination in 2020.
Ms Williamson said she supports stricter gun laws, freedom of choice and universal health care.
Robert F Kennedy Jr: A member of the famed Kennedy dynasty, Robert F Kennedy Jr became a leading voice in the anti-vaccine movement and has been criticised for using his family's name in his work.
He also has appeared at events that support false claims that the 2020 election was stolen.
Republican Party
Donald Trump: The former president launched his third presidential campaign last year as several investigations took aim at his businesses, his role in the January 6 insurrection and more.
He suffered the ignominy of becoming the first president to be criminally charged after Manhattan prosecutors accused him of falsifying business records to cover up hush money paid to an adult film star during the 2016 election.
But Mr Trump remains the front-runner in the Republican field and has spent much of his post-presidency time denouncing Mr Biden's administration.
Mike Pence: The former vice president who served under Mr Trump is running for presidency for the first time.
His candidacy makes for a political fight against his former boss, who is leading the Republican race for the party's nomination.
Ron DeSantis: Florida Governor Ron DeSantis is seen as Mr Trump's biggest rival for the party's nomination after he officially launched his campaign for the Republican party's nomination in late May.
"My pledge to you is this: If you nominate me, you can set your clock to January 20, 2025, and high noon, because on the west side of the US Capitol, I will be taking the oath of office as the 47th President of the United States," he said.
Nikki Haley: Indian-American politician Nikki Haley was UN ambassador under Mr Trump's administration after serving as South Carolina governor from 2011 to 2017.
Ms Haley said it was time for a new generation of leaders when she announced her candidacy on February 15 and vowed to challenge Iran and China.
Tim Scott: The senator from South Carolina threw his hat into the ring in May.
Mr Scott is the only black Republican in the Senate. He was a businessman before entering politics.
Chris Christie: The former governor of New Jersey announced his campaign in June.
Mr Christie has been the the only Republican candidate to publicly challenge Mr Trump, after he worked closely with the former president for years.
Asa Hutchinson: The former Arkansas governor announced his presidential bid on April 2 while also saying Mr Trump should not seek office.
Mr Hutchinson has grown more critical of the former president since leaving office.
Will Hurd: One-time CIA officer and former member of the House of Representative, Mr Hurd launched his campaign in June as a moderate Republican critical of Mr Trump.
He was also briefly the only black Republican in the House before his term ended in January 2021.
Vivek Ramaswamy: "Anti-woke” activist Vivek Ramaswamy announced his long-shot bid for the Republican nomination on February 21, saying that he would step down from his role at Strive Asset Management to pursue his White House campaign.
The former biotechnology executive first made national headlines in 2021 with his book Woke Inc: Inside Corporate America's Social Justice Scam.
Larry Elder: Conservative radio host Larry Elder ran a failed recall campaign against California's Democratic governor Gavin Newsom in 2021.
“We can enter a new American Golden Age, but we must choose a leader who can bring us there. That’s why I’m running for president,” Mr Elder said in his announcement.
Perry Johnson: Businessman Perry Johnson also announced a long-shot bid for the Republican nomination after he failed to get on the ballot for the 2022 Michigan gubernatorial race.
Who else could run?
Though the Democratic field is largely complete with Mr Biden's candidacy, the Republican field is expected to become more crowded.
Others who are reportedly considering campaigns are Virginia Governor Glenn Youngkin and former national security adviser John Bolton.
Other political parties in the US – such as the Libertarian and Green parties – will also select their candidates during the 2024 primary season, although any ticket emerging from those parties is unlikely to gain major traction in the general election.
Cornel West: The political activist and academic Cornel West announced his run for presidency as a third-party candidate with the People's Party, making him the second black candidate to join the field after Mr Scott.
He tweeted that his goals will lie in "fighting to end poverty, mass incarceration, ending wars and ecological collapse, guaranteeing housing, health care, education and living wages for all".
