US President Joe Biden said on Sunday that he has ended his re-election bid amid intense pressure from Democratic leaders who have sounded the alarm that his path to defeating former President Donald Trump in November has faded.

The president's historic withdrawal puts the 2024 race — already affected by a horrific attempt on Trump's life — in an even more unpredictable position, with Vice President Kamala Harris seen as the best Democratic candidate to replace Biden at the top of the party's ticket.

Biden made the announcement from his home in Rehoboth Beach, Delaware, where he has isolated himself since testing positive for Covid-19 on Thursday night.

“It has been the greatest honor of my life to serve as your president,” Biden said in a written statement. “While I intend to run for re-election, I believe it is in the best interests of my party and my country for me to step down and focus solely on my duties as President for the remainder of my term.”

Biden did not immediately endorse a successor. He said he would speak to the nation later this week to provide more details about his decision.

It represents an unusual turn for Biden, who for three weeks has remained defiant in the face of growing calls from Democratic lawmakers to withdraw after a disastrous June 27 debate with Trump that drew scrutiny over the president's mental fitness.

Biden's exit came after he received grim warnings from Senate Majority Leader Chuck Schumer and House Democratic Leader Hakeem Jeffries that his candidacy could lead to heavy losses for Democrats in the Senate and House of Representatives.

More than 30 Democratic members of Congress have called on Biden to step down, and former President Barack Obama is said to have conveyed similar concerns to Democratic allies about Biden's prospects for victory over Trump. Democratic donors from Hollywood to Wall Street also opposed Biden continuing his re-election bid.

The decision turns the 2024 election upside down, less than 110 days before Election Day, as members of the Democratic National Committee are now tasked with choosing an alternative candidate to confront Trump, whose lead in opinion polls has swelled while Democrats have been fighting internally.

According to all experts, Vice President Harris is now the favorite to replace Biden as the Democratic nominee, but there could also be a seat for the party's Democratic governors, including Gretchen Whitmer of Michigan, Josh Shapiro of Pennsylvania, and Gavin Newsom of California.

Biden became the first sitting president not to seek re-election since Lyndon Johnson, who surprised the nation in 1968, amid national turmoil and unrest within the Democratic Party over the Vietnam War, by deciding not to run for a full second term.

Biden (81 years old) has been facing Americans' concerns about his age since he took office, but the matter turned into a state of panic for Democrats after the first debate last month with Trump, the Republican candidate. Biden's voice sounded soft, he had difficulty completing sentences and finishing thoughts, and he failed to refute many of Trump's claims on the debate stage.

Biden's campaign has been in a state of steady collapse over the past few weeks, with doubts about his future. Instead of focusing solely on Trump, Democrats spent a great deal of time and energy debating whether Biden could defeat his predecessor.

Fundraising for Biden's campaign has declined significantly in recent days, as Biden has not only fallen behind in the key states that will decide the elections, but it appears that his growing popularity decline is putting the last Democratic strongholds, such as Virginia, in favor of Trump.

Biden's departure will soon mean the end of a five-decade run in Washington that began in 1972 with a surprise victory for the US Senate in Delaware. He served as a senator for 36 years, then as Obama's vice president from 2009 to 2017. Biden returned to public life to run against Trump in the 2020 presidential election, beating Trump 51%-47% in the popular vote.

First Lady Jill Biden on Sunday reposted the president's message with heart emojis.