President Joe Biden on Sunday announced he will not seek a second term following a revolt by top congressional Democrats and donors in reaction to a debacle of a debate against former President Donald Trump, the GOP nominee.

“It has been the greatest honor of my life to serve as your President. 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,” Biden said in a letter posted on social media platform X, formerly Twitter. “I will speak to the Nation later this week in more detail about my decision.

“For now, let me express my deepest gratitude to all those who have worked so hard to see me reelected,” Biden added. “I want to thank Vice President Kamala Harris for being an extraordinary partner in all this work.”

In a subsequent tweet, Biden offered his explicit endorsement of Harris.

“Today I want to offer my full support and endorsement for Kamala to be the nominee of our party this year. Democrats — it’s time to come together and beat Trump. Let’s do this,” Biden wrote in a post from his personal account.

In a statement about two hours later, Harris praised Biden for his “selfless and patriotic act.”

“I am honored to have the President’s endorsement and my intention is to earn and win this nomination,” Harris said in a statement. “I will do everything in my power to unite the Democratic Party — and unite our nation — to defeat Donald Trump.”

The 46th commander in chief became the first president since the 36th, Democrat Lyndon B. Johnson, to not seek a second term. Some Democratic lawmakers and strategists since the June 27 prime-time debate had suggested Biden step aside and allow a younger Democrat, possibly Harris, to pursue the party’s nomination.

[These Democrats have called on Biden to quit the race]

Sen. Joe Manchin III, I-W.Va., a former Democrat who is retiring after this Congress, on Sunday called on Biden to step aside during a talk show appearance. Democrats running in tough races in recent days have increasingly piled on, including Sens. Sherrod Brown of Ohio and Jon Tester of Montana.

Others who stopped short of calling on Biden to quit said he needed to demonstrate the debate was an aberration. But a series of follow-up events, including a full news conference, one-on-one network interviews on ABC and NBC, and a NATO summit where he used the president of Russia’s name when introducing the president of Ukraine, did not calm critics, especially as new polls showed him falling behind in battleground states. 

Top Democrats like House Minority Leader Hakeem Jeffries, Senate Majority Leader Charles E. Schumer — both of New York — and former Speaker Nancy Pelosi of California did not forcefully deny reports that they had told Biden he could not win another term and risked the party’s chances of flipping the House and holding onto the Senate. Nearly three dozen House and Senate members, including Pelosi allies Adam B. Schiff and Zoe Lofgren, have called for the president to “pass the torch.”

Trump’s campaign issued a blast email shortly after Biden’s letter posted, declaring the president “just quit the race in COMPLETE DISGRACE.”

Republicans in Congress said that if Biden couldn’t campaign, he shouldn’t remain in office, and accused Democrats of covering up for him.

“This is a scandal of historic proportions – our president is incapacitated, Democrats knew, and they lied to the American people to cover it up,” National Republican Congressional Committee Chairman Richard Hudson, R-N.C., said in a statement that was likely prewritten since it arrived only moments after Biden’s announcement. “Voters will neither forgive nor forget the ultimate betrayal of their trust. Judgment day is coming in November.”

Speaker Mike Johnson, R-La., said on X that Democrats who forced Biden off the ticket “invalidated the votes of more than 14 million Americans.” Johnson had said on Fox News earlier Sunday that there would be legal challenges to substituting Biden.The president’s announcement came hours after a new Detroit Free Press poll in Michigan, a state he won in 2020 and would likely have to win again to have any chance of defeating Trump, showed Biden trailing by 7 percentage points, 49 percent to 42 percent.

The president tested positive for COVID-19 while on a trip to Nevada, during which he told BET News that he would step aside if he developed a serious medical condition. His White House physician had said his COVID-19 symptoms were “mild.”

In the debate, Biden’s voice sounded raspy during his first face-off with Trump in four years — especially at the onset. His answers were rambling and difficult to follow until he found his footing around the midway mark of the 90-minute verbal sparring session. He has since blamed jet lag after two European trips, a Los Angeles fundraiser and a subsequent cold.

In interviews, Biden has referred to a “mistake” in his debate preparation — but he and his top aides have never fully clarified what those were, including by not responding to inquiries.

At one point early in the debate, Biden froze mid-answer. 

“What I’ve been able to do with the, with, with, with the COVID, excuse me. With dealing with everything we have to do with,” Biden said, looking down at his lectern, adding after several seconds of silence: “Look, if we finally beat Medicare.”

The president who still boasts about his foreign policy experience multiple times appeared to mix up Trump and Russian President Vladimir Putin.

“If you take a look at what Trump did in Ukraine, he, this guy told Ukraine, he told Trump, do whatever you want, and do whatever you want. And that’s exactly what Trump did to Putin,” Biden said.

It was not immediately clear who would replace Biden at the top of the party’s ticket. The Democratic National Convention is slated to begin Aug. 19 in Chicago.

Biden has been trailing Trump for months in most national polls by slim margins, but by larger margins in six key swing states. Analysts of all political stripes expect Trump to get at least a small polling bounce after he survived a would-be assassin’s bullet at a July 13 campaign rally in Butler, Pa., and a mostly upbeat Republican National Convention that ended July 18 in Milwaukee.

“Biden had a very low bar going into the debate and failed to clear even that bar,” Julián Castro, a former Democratic secretary of Housing and Urban Development and San Antonio mayor, wrote on social media platform X shortly after the debate wrapped. “He seemed unprepared, lost, and not strong enough to parry effectively with Trump, who lies constantly.”

The chorus among Democratic lawmakers, donors and strategists only grew from there.

Ahead of Trump’s speech accepting the GOP nomination on July 18, a group of Biden campaign officials and Democratic lawmakers who were in Milwaukee had assured reporters that the president would remain in the race.

Sen. Alex Padilla, D-Calif., told reporters there that he “couldn’t disagree more on this issue” with Schiff, who’s favored to become the state’s junior senator come 2025.

Briana Reilly contributed to this report