Born in November 1942, Joe Biden is currently the oldest incumbent president in US history and has an approval rating of just over 40.
Donald Trump, the man he defeated two years ago, has just announced that he will run for president again.
But both are unpopular with a significant number of voters, and polls show a majority of Democrats want to nominate someone other than Mr Biden, the 46th US president.
This could provide an opportunity for the younger generation of Democrats.
Kamala Harris
A former prosecutor and then attorney general of California and US senator, the 58-year-old in 2020 became the first female, first Asian-American, and first black vice president in US history.
Last year, she served as acting president for 85 minutes while Mr Biden underwent a colonoscopy – possibly the closest she has ever been to the Oval Office.
Ms Harris is not even as popular as the president, and some voters question her qualifications.
Since taking office, she has been tasked with some of the administration’s most difficult issues, including the migrant crisis at the southern border of the United States. Constant staff turnover and low morale in the vice president’s office have only made matters worse.
But the vice president’s supporters – including an online fan base known as the “K-Hive” – say she has been treated unfairly and sexist.
Gavin Newsom
If Vice President Harris was once the front-runner to succeed President Joe Biden, another California politician — Governor Gavin Newsom — is the most high-profile contender for 2024.
Mr. Newson, 55, first gained national attention when, as mayor of San Francisco in 2004, he issued same-sex marriage licenses in violation of state law.
A liquor businessman, he was elected governor of his home state in 2018, and has positioned himself as a progressive against the conservative Trump administration.
He was praised for his decisive leadership early in the pandemic, but when images emerged of him breaking his own Covid laws, there were calls for his recall before his term ended.
However, he was re-elected earlier this month and is entering a second term.
Pete Buttigieg
Of the 28 Democrats Mr. Biden defeated to become the party’s 2020 nominee, few shined like Pete Buttigieg.
Despite being unknown in politics, the 40-year-old was favored over many seasoned politicians, before eventually dropping out of the race.
A Rhodes Scholar at Oxford, a Harvard graduate, and a U.S. Navy veteran in Afghanistan, Buttigieg came out as gay in 2015 while serving as mayor of South Bend, a small industrial town of about 100,000 in Indiana.
Known to his supporters as “Mayor Pete,” he was picked as Biden’s secretary of transportation.
Bernie Sanders
If Mr. Biden is considered too old, then the nomination of Bernie Sanders – the senator who was re-elected this year at 81 years old – to run for president in 2024 is even more absurd to many.
But many voters still see the longtime lawmaker as a beacon of a growing left-wing movement in the United States.
Mr. Sanders – an independent lawmaker who votes for the Democratic Party – narrowly defeated Democratic heavyweight candidate Hillary Clinton in the 2016 presidential election. This year, he was elected to the United States Senate, representing Vermont.
Coming in second again in 2020 behind Mr Biden, Mr Sanders, a self-described “democratic socialist”, has since worked to influence administration policies, with moderate success.
But his message that Democrats have done too little to appeal to young and working-class voters remains true, and his supporters are hoping his third attempt at the White House will be successful.
Others may run for office.
Alexandria Ocasio-Cortez: Often referred to as AOC, the youngest woman ever in Congress will turn 35 — the minimum age to become US President — a month before the 2024 election. A favorite of the progressive left, Ocasio-Cortez has big ideas and a following, but is reluctant to talk about her future.
Ro Khanna: A self-described ‘progressive capitalist’, this Indian-American congressman represents Silicon Valley in Congress. He has said he will not run if Mr Biden is nominated.
Amy Klobuchar: The 62-year-old Minnesota senator has kept a low profile in the 2020 presidential race, but she has close ties to the Biden administration and holds a key Democratic power-brokering position in the Senate.
Cory Booker: Another candidate in the 2020 presidential race, the 53-year-old black senator from Jew Jersey was praised earlier this year for an emotional speech celebrating the historic moment of having the first black woman on the Supreme Court.
Elizabeth Warren: The 73-year-old Massachusetts senator recently spoke out on behalf of women angry about the rollback of abortion rights in the US.
Gretchen Whitmer: The 51-year-old Michigan native faced a kidnapping plot during her first term as governor, and earlier this month resumed her second term. She said she has no plans to run for president.
JB Pritzker: The 57-year-old Illinois politician, whose family owns the Hyatt hotel chain, is the wealthiest governor in the country. In recent speeches, he has targeted Mr. Trump, accusing him of “treasonous insurrection.”
Jared Polis: The first US governor to marry a same-sex partner, Colorado’s 47-year-old Polis has won praise for his handling of the pandemic and just won re-election easily.
Phil Murphy: A Goldman Sachs financier and former US ambassador to Germany, the 65-year-old New Jersey governor has worked closely with both Republican and Democratic administrations in Washington.
Every election, observers have speculated that former First Lady Michelle Obama or former Secretary of State Hillary Clinton, a two-time failed presidential candidate, might enter the race.
But while both women are popular with voters, neither has expressed any intentions. In fact, Michelle Obama recently told BBC News that this was her least favourite question.