Mr. Biden, 81, announced his withdrawal after a disastrous debate performance against Mr. Trump cemented public concerns about his age and touched off widespread panic among Democrats about his ability to prevent the former president from reclaiming power. Democratic congressional leaders petrified by dismal poll numbers pressed Mr. Biden to gracefully exit, angry donors threatened to withhold their money and down-ballot candidates feared he would take down the whole ticket.
No sitting president has dropped out of a race so late in the election cycle in American history, and Ms. Harris and any other contenders for the nomination will have just weeks to earn the backing of the nearly 4,000 delegates to the Democratic National Convention. While the convention is scheduled to take place in Chicago from Aug. 19 to Aug. 22, the party had already planned to conduct a virtual roll call vote before Aug. 7 to ensure access to ballots in all 50 states, leaving little time to assemble support.
Mr. Biden’s campaign for a second term collapsed in swift and stunning fashion after leading Democrats concluded that he would be unable to defeat Mr. Trump in the fall. During their nationally televised debate last month, Mr. Biden, the oldest president in American history, appeared frail, hesitant, confused and diminished, losing a critical opportunity to make his case against Mr. Trump, a convicted felon who tried to overturn the last election.
Although Mr. Trump, 78, is just a few years younger than Mr. Biden, he came across as forceful at the debate even as he made repeated false and misleading statements. Questions have been raised about Mr. Trump’s own cognitive decline. He often rambles incoherently in interviews and at campaign rallies and has confused names, dates and facts just as Mr. Biden has. But Republicans have not turned against him as Democrats did against Mr. Biden.
The president’s age was a primary concern of voters long before the debate. Even most Democrats told pollsters more than a year ago that they thought he was too old for the job. Born during World War II and first elected to the Senate in 1972 before two-thirds of today’s Americans were even born, Mr. Biden would have been 86 at the end of a second term.
Mr. Biden consistently maintained that his experience was an advantage, enabling him to pass landmark legislation and manage foreign policy crises. He maintained that he was the Democrat best equipped to defeat Mr. Trump given that he did so in 2020.
But his efforts to reassure Democrats that he was up to the task following the damaging debate failed to shore up support. Instead, his slowness to reach out to party leaders and some of the answers he gave in interviews only fueled internal discontent.
In bowing out, Mr. Biden became the first incumbent president in 56 years to give up a chance to run again. With six months remaining in his term, his decision instantly transformed him into a lame duck. But he can be expected to use his remaining time in office to try to consolidate gains on domestic policy and manage ongoing wars in Europe and the Middle East.
His announcement signaled the end of an improbable life in public office that began more than half a century ago with his first election to the New Castle County Council in Delaware in 1970. Over the course of 36 years in the Senate, eight years as vice president, four campaigns for the White House and more than three years as president, Mr. Biden has become one of the most familiar faces in American life, known for his avuncular personality, habitual gaffes and resilience in adversity.
Yet the backslapping deal-maker has struggled to translate decades of good will into the unifying presidency he promised. He led the country out of the deadliest pandemic in a century and the resulting economic turmoil, but his hopes of healing the rifts that widened under Mr. Trump have been dashed. American society remains deeply polarized and his predecessor is still a potent force in stirring the forces of division and emboldening white supremacists and anti-Semites.
While he has spent most of his elective career seeking the political center, Mr. Biden advanced an expansive progressive agenda after taking office that his allies likened to Franklin D. Roosevelt’s New Deal or Lyndon B. Johnson’s Great Society. Working with the narrowest of partisan margins in Congress, he scored some of the most ambitious legislative victories of any modern president in his first two years.
Among other measures, he pushed through a $1.7 trillion Covid-19 relief package; a $1 trillion program to rebuild the nation’s roads, highways, airports and other infrastructure; and major investments to combat climate change, lower prescription drug costs for seniors, treat veterans exposed to toxic burn pits and build up the nation’s semiconductor industry. He also signed legislation meant to protect same-sex marriage in case the Supreme Court ever reversed its decision legalizing it.
He also appointed Ketanji Brown Jackson to become the first Black woman on the Supreme Court and installed more than 200 other judges on lower federal courts despite the razor-thin control of the Senate, more than any other president to this point of his tenure in the modern era. Roughly two-thirds of his choices were women and roughly two-thirds were Black, Hispanic or members of other racial minorities, meaning he has done more to diversity the federal bench than any president.
Some of the major bills Mr. Biden passed drew Republican votes, but his string of legislative successes effectively ended with the 2022 midterm elections when Republicans won a narrow majority in the House, even if not scoring the “red wave” sweep that they had anticipated. Mr. Biden has been left to play defense ever since, successfully forging agreements with Republicans to avoid government shutdowns and national default but accomplishing little else more proactive.
On the international front, Mr. Biden revitalized international alliances that frayed under Mr. Trump, rallying much of the world to stand against Russia’s unprovoked invasion of Ukraine. Despite opposition by Mr. Trump and his allies, Mr. Biden secured tens of billions of dollars to arm Ukrainian forces and provide economic and humanitarian aid, although some critics have complained that he has been too slow to send the most sophisticated weaponry out of fear of escalation.
Mr. Biden supported Israel in its war against Hamas following the Oct. 7 terrorist attack, but he has grown frustrated with Prime Minister Benjamin Netanyahu, saying that Israel is not doing enough to avoid civilian casualties and guarantee humanitarian aid to Gaza. Mr. Biden alienated many in his own party by not doing more on behalf of Palestinians and then angered supporters of Israel by refusing to ship certain weapons if they were to be used for an all-out assault on the Gaza city of Rafah.
Mr. Biden’s decision to pull all forces out of Afghanistan after 20 years, carrying out an agreement that Mr. Trump had struck with the Taliban, led to a debacle in the summer of 2021. Taliban forces swiftly took over the country, fleeing Afghans swarmed American airplanes taking off from Kabul and a suicide bomber killed 13 American troops and 170 Afghans during the withdrawal.
The president has also struggled to secure the southwestern U.S. border, where illegal migration has soared, and to stabilize the post-pandemic economy, in which inflation rose to its highest level in four decades and gas prices shot up to record levels. While inflation has fallen to 3 percent from its peak of 9 percent and unemployment at 4.1 percent remained near a half-century low, many Americans remain unsettled by economic anxiety.
Mr. Biden’s overall approval rating remained mired at an anemic 38.5 percent, according to an aggregation of polls by the political analysis website fivethirtyeight.com, lower than nine of the last 11 presidents who made it this far into their terms. His aides brushed off such data, noting that Mr. Biden surprised forecasters in the 2020 primaries, as did Democrats in the 2022 midterm elections.
Mr. Biden has noticeably slowed down in recent years. His gait has grown stiffer, his voice softer, and his energy level at times has diminished. He mangles his words, gets momentarily confused or forgets names or words that he tries to summon. He exercises most days and does not drink; doctors have pronounced him fit for duty. Aides and others who deal with him have long insisted that he remained sharp and informed in private meetings.
His decision to withdraw makes him an outlier in American history. Only three presidents have served four years or less without seeking a second term, all of them during the 19th century: James K. Polk, James Buchanan and Rutherford B. Hayes. Several others wanted another term but failed to secure their party’s nomination.
The last president who had the option to run again given the two-term limit in the 22nd Amendment but chose not to was Lyndon Johnson, who served the remainder of John F. Kennedy’s term following his 1963 assassination and then won a full term of his own the next year, only to back out of another race in 1968 amid the war in Vietnam.