On Sunday, US President Joe Biden announced that he is withdrawing from the reelection race against Donald Trump, a historic decision that adds new uncertainty to the already tumultuous 2024 White House race. He endorsed Vice President Kamala Harris as the Democratic candidate.

"It has been the greatest honor of my life to serve you as president," the 81-year-old Democrat stated in a letter on X, posted while he was recovering from COVID-19 at his beach house in Delaware.

"While it has been my intention to seek reelection, I believe it is in the best interest of my party and the country for me to step down and focus solely on fulfilling my duties as President for the remainder of my term."

Biden mentioned that he would "speak to the nation later this week in more detail about my decision."

This decision throws the Democratic Party into turmoil as they scramble to find a new candidate for the November election, with Vice President Kamala Harris emerging as the frontrunner.

Biden's move makes him the first president in US history to withdraw so late in an election race and the first to step down due to concerns over his mental acuity and health.

Biden resisted calls to step down for over three weeks following the shocking June 27 debate, at one point asserting that only the "Lord Almighty" could convince him to withdraw.

In an effort to prove his capability, Biden gave several interviews and held a "big boy" press conference where he took numerous questions but made further gaffes, including calling Kamala Harris "Vice President Trump."

A growing chorus within his own party, from donor and actor George Clooney to former president Barack Obama, ultimately sealed his fate.

Biden's decision came shortly after he was diagnosed with COVID-19, which forced him off the campaign trail and into isolation.

This announcement marks a tense and chaotic period in the US election, with Trump surviving an assassination attempt at a campaign rally on July 13.

Biden joins a small group of US presidents who decided to step down after just one term, with the last being Lyndon Johnson in 1968, a year also marked by political turmoil and violence. Johnson's replacement, then-vice president Hubert Humphrey, lost heavily to Richard Nixon.

Democrats are now placing their hopes on Harris to fare better and prevent Trump, a convicted felon, from making a sensational comeback to the Oval Office.

In recent weeks, the Biden campaign has reportedly been quietly conducting voter surveys to measure Harris's performance against Trump.

While Harris initially struggled to make an impact in her first years in the White House, she has emerged as a strong performer on the campaign trail in the last year, focusing on key messages such as abortion rights.

The former prosecutor has also highlighted her life story as the first woman and the first person of Black and South Asian origin to hold the vice presidency.

Biden took office in January 2021, pledging to heal the "soul of America" after four tumultuous years under Trump and the shock of the January 6 Capitol assault by Trump supporters.

Despite a reputation for verbal flubs, Barack Obama's former vice president successfully pushed through a massive COVID recovery plan and a green industry scheme.

US allies welcomed his declaration that "America is back" after Trump's disruptions to international alliances, and his strong support for Ukraine during Russia's 2022 invasion.

However, he faced criticism over the disastrous US withdrawal from Afghanistan and inflation that led many Americans to overlook otherwise positive economic indicators.