U.S. President Joe Biden, who has been in the White House since 2021, faces two long-shot challenges to be his Democratic Party's nominee in the 2024 election. The winner will take on the victor of the Republican Party's nominating race, in which former President Donald Trump is by far the front-runner.

Here is a list of the Democratic hopefuls.

JOE BIDEN

Biden, 80, already the oldest U.S. president ever, will have to convince voters he has the stamina for another four years in office, amid concerns about his age and poor approval ratings. Biden allies say he feels he is the only Democratic candidate who can defeat Trump.

In announcing his candidacy, he declared it was his job to defend American democracy, and referred to the deadly Jan. 6, 2021, attack on the U.S. Capitol by Trump supporters. Biden does not face a serious threat from a Democratic challenger.

ROBERT KENNEDY JR.

An anti-vaccine activist, Kennedy, 69, is making a long-shot bid to challenge Biden for the Democratic nomination. He is the son of U.S. Senator Robert F. Kennedy, who was assassinated in 1968 during his own presidential bid.

Kennedy was banned from Instagram for spreading misinformation about vaccines and the COVID-19 pandemic, but was reinstated. He lost a legal bid to force YouTube owner Google to reinstate videos of him questioning COVID vaccines' safety.

MARIANNE WILLIAMSON

The best-selling author and self-help guru has launched her second, long-shot bid for the White House on a platform of "justice and love." She ran as a Democrat in the 2020 presidential primary but dropped out of the race before any votes had been cast. She launched her latest campaign on March 23.

(Reporting by Costas Pitas; editing by Jonathan Oatis)