Biden drops out of 2024 presidential race

President Joe Biden is leaving the 2024 race after a halting debate performance against Donald Trump led to questions from Democrats about his age, ability to carry out his campaign and whether he could serve a second term.

Biden said in a statement posted Sunday that he will "stand down."

"It has been the greatest honor of my life to serve as your President," he wrote, in part, in a letter posted on X. "And 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 stand down and to focus solely on fulfilling my duties as President for the remainder of my term."

"I will speak to the Nation later this week in more detail about my decision," he added. First lady Jill Biden reposted her husband's post announcing he's dropping out with a hearts emoji.

In another post on X, Biden gave his "full support and endorsement" for Vice President Kamala Harris to be the Democratic Party's nominee.

The stunning move upends what has been a long general election rematch between Biden and Trump, both of whom handily won their party's primaries, with less than four months until the November contest.

While concerns about Biden's age plagued him since he launched his reelection campaign in April 2023, they reached a fever pitch following his showdown with Trump at the CNN debate in Atlanta in late June.

Biden, who at 81 is the oldest sitting president in history, spoke with a hoarse voice that his team attributed to a cold. But coupled with his meandering answers and inability to hit Trump hard on key Democratic issues, his performance left some pundits and politicians speechless.

The White House and campaign chalked up the performance as a "bad night." Biden defiantly insisted he would remain in the race, repeatedly telling Democrats he was the best option to defeat Trump.

"I convinced myself of two things. I'm the most qualified person to beat him, and I know how to get things done," Biden told ABC News anchor George Stephanopoulos in his first post-debate television interview.

"Look. I mean, if the Lord Almighty came down and said, 'Joe, get outta the race,' I'd get outta the race. The Lord Almighty's not comin' down," Biden said at the time.

But early polling showed the debate's negative impact. In 538's national polling average, Trump now leads by 2 percentage points over Biden, while the two candidates were just about tied on the day of the June 27 debate.

And despite Biden and his campaign's furious attempts at damage control, including a press conference after concluding a NATO summit in Washington where he took reporter questions for nearly an hour and tried to make the case he must "finish the job," a steady drumbeat of Democratic lawmakers and public figures called on him to step aside as the nominee.

The number of congressional Democrats who called on him to step aside rose to 40 by the time Biden announced his decision to leave the race.

"The one thing I know for sure is that we can do better than Joe Biden as a person who can deliver our message in this election cycle," Rep. Adam Smith, D-Wash., had previously told ABC News. "And we have time to do that. And we should."

Biden was also taken off the campaign trail these past few days due to a case of COVID-19, which he is recovering from at his residence in Rehoboth, Delaware.

To emphasize how closely held Biden's decision to exit the race was, a source familiar with the matter told ABC Senior White House Correspondent Selina Wang that Biden informed his senior team that he changed his mind about staying in the race at 1:45 p.m. Sunday.

Biden's letter came out at 1:46 p.m. -- so his staff was told just one minute before the public announcement that he was dropping out.

Before Biden's revelation Sunday, House Democratic Leader Hakeem Jeffries and Senate Majority Leader Chuck Schumer had publicly said they supported Biden making a decision during the party's turmoil. But privately, they were said to have been sympathetic to the view held by a growing number of congressional Democrats that Biden was on a path to lose to Trump.

Schumer went to Delaware to speak to Biden and made the case it would be best if Biden dropped out of the 2024 presidential race, ABC News Chief Washington Correspondent Jonathan Karl reported.

As scrutiny of Biden intensified, focus increased on Vice President Kamala Harris as a possible choice to replace him as the Democratic nominee.

“I wouldn’t have picked her unless I thought she was qualified to be president,” Biden said of Harris at his press conference on July 11.

The Democratic Party's dysfunction stood in sharp contrast to the steadfast party unity shown to Trump, despite his own struggles that include a historic conviction, during the Republican National Convention in Milwaukee, Wisconsin.

As he accepted his party's nomination, Trump spoke of the "love in the room" and enthusiasm for what's to come.

"I am running to be president for all of America, not half of America, because there is no victory in winning for half of America," Trump said.

Harris, in a statement Sunday, thanked Biden for his "decades of service to our country" and said she "will do everything in my power to unite the Democratic Party -- and unite our nation -- to defeat Donald Trump and his extreme Project 2025 agenda."

"I am honored to have the President’s endorsement and my intention is to earn and win this nomination," Vice President Harris said.

ABC News' Selina Wang and Fritz Farrow contributed to this report.