Joe Biden's withdrawal upends what was already a White House race for the ages, but it will rattle Donald Trump, too -- forcing him to recalibrate a campaign that was focused almost entirely on his former opponent.
For months Trump and his allies have been playing on concerns that the 81-year-old Biden may no longer be fit for office, gleefully sharing video clips of every stammer, rhetorical gaffe and red carpet stumble.
He was frequently a target of Republican mockery and scorn at the Republican National Convention in Milwaukee, where Trump's newly announced running mate J.D. Vance called him "Fake Scranton Joe."
But with the Democrat no longer in the race, the Trump operation finds itself pushed into a strategic pivot, forced now to shift its messaging to fit a contest with no incumbent and a yet-to-be-confirmed opponent, although Biden did endorse Vice President Kamala Harris on Sunday as he pulled out of the race.
"Biden withdrawing is bad news for Trump," Henry Olsen, a senior fellow at the conservative Ethics and Public Policy Center think tank, told AFP.
"Biden has the lowest job approval of any first-term president at this stage of his presidency in polling history and is also irretrievably burdened by his age. It's much better for Trump to run against him than any conceivable opponent."
Trumpworld had been playing down the chances of Biden withdrawing, but behind-the-scenes aides have been consumed by the contingencies, preparing a brutal assault on the veteran Democrat's heir apparent, Harris.
"Nothing fundamentally changes" Jason Miller, one of Trump's closest advisors, told AFP during the Republican convention, saying that any "radical liberal" Democratic opponent, Harris or otherwise, shares "the responsibility for the failure of destroying our economy."
Harris, a 59-year-old former California senator is not a shoo-in and could face competition from multiple leading Democrats in Congress and the nation's 23 Democratic governors.
"I'm going to show up and I'm going to campaign -- whether it's him or somebody else," Trump told a radio network in Virginia before Biden's announcement, pointing to polls showing him doing as well or better against other Democrats.
Clash of cultures
Voters have been telling pollsters for months they want younger political leaders, and a ticket topped by a relatively youthful swing state governor, for example, would be a threat to Trump, who would be 82 at the end of a second term.
A campaign led by Harris and backed up by a moderate midwestern running mate could present the biggest danger though, helping turn out more women, who historically vote in greater numbers than men and are a weakness for Trump.
Harris would also give Democrats a chance to redefine the race at their convention in Chicago in August as a clash of cultures between a former prosecutor and a convicted felon.
And Harris ensures that abortion rights -- one of her biggest domestic priorities and another vulnerability for Trump and the Republicans -- remains a crucial election issue.
Trump's new, serious focus on the vice president was demonstrated by his bestowal on her of one of his famous nicknames, referring to her on social media recently as "Laffin' Kamala Harris."
'Destruction and chaos'
It is the disastrous June presidential debate in Atlanta that proved the catalyst for Biden's withdrawal.
A new survey from Democratic polling form Public Policy Polling released Thursday found that Harris -- with the right running mate -- likely can defeat Trump and Vance in Pennsylvania and Michigan, two of the three "Blue Wall" states seen as critical to electing a Democratic president.
The vice president has the disadvantage of incumbency, though, meaning Trump can pin on her anything that was considered a weakness for Biden -- including the border crisis, on which Harris led the administration's early efforts.
Several Democratic rising stars have been floated as alternatives, including governors Josh Shapiro, Gretchen Whitmer and Gavin Newsom.
Newsom, of California -- who has demonstrated a willingness to go toe-to-toe with top Republicans -- would be unlikely to be intimidated by Trump's broadsides.
Whitmer was considered for the Biden ticket in 2020 and has since spearheaded a Democratic resurgence in Michigan, while Pennsylvania's Shapiro is another serious contender as chief executive of a critical swing state.
Whoever becomes the nominee, Trump will likely spend the rest of the campaign pushing them on their past defenses of Biden, accusing them of covering up the president's decline.
"The destruction and chaos created by the Biden administration isn't just on Crooked Joe -- it's on the entire Democrat Party," the Trump team said in a recent edition of its daily circular.
"None have been worse than Kamala Harris, who has lied repeatedly -- presumably putting her own position above the security of the American people."
AFP adds:
Biden, stubborn president who fought a battle too far
Joe Biden wanted to save the "soul of America" from Donald Trump, but his stubborn defiance of the march of time may have cleared his rival's path back to power.
Biden caved in to growing pressure Sunday and announced he is dropping out of the presidential race, amid concerns over his mental acuity and ability to beat Trump and serve four more years.
As he fought for his political survival after a disastrous debate, the 81-year-old Democrat repeatedly cited his family's mantra that "when you get knocked down, get back up again."
From playground punch-ups to a stutter to terrible family tragedies, Biden had long seen his life story as a series of comebacks against impossible odds.
And it was his triumph four years ago against Trump that convinced Biden that, despite being the oldest president in US history, he was the only one who could do it again -- until he threw in the towel on Sunday.
Overcoming his reputation as a gaffe machine, Biden initially lived up to his goal as a "unifier in chief" after the Trump years and the shock of the January 6, 2021, attack on the US Capitol.
But the question of his age always loomed large.
Biden eventually joked about it but always denied it was an issue, even after a debate where his rambling answers and listless stare sparked a revolt by Democrats.
A mix of pride and his conviction that Trump was a threat to democracy kept Biden fighting until it was, perhaps, too late.
Franklin Foer, author of a book on the Biden presidency, wrote recently that "humiliation -- and its transcendence -- is Biden's origin story."
"Right now it is his psychological prison, a mental habit that might doom American democracy," he wrote in the Atlantic.
'Cruel losses'
That outlook was largely formed by a hardscrabble childhood in Scranton, Pennsylvania, in the American rust-belt.
Biden was part of a close-knit Irish Catholic family -- he was just the second Catholic US president after his hero John F. Kennedy -- that was known for its intense pride.
His mother Jean told the young Joey and his siblings every day that "nobody was better than a Biden," Ben Cramer wrote in his book "What It Takes," about the 1988 US election campaign.
He was also known for never backing down.
"He decided to fight... BANGO -- he'd punch the guy in the face," Cramer wrote.
One affliction Biden famously had to battle was a childhood stutter.
Repeatedly humiliated at school, the young Biden ended up teaching himself how to speak smoothly by sheer determination, repeating phrases again and again into the mirror.
But Biden's biggest test was yet to come.
In 1972, he was only 29 and had just won an unlikely victory to be elected senator for Delaware when his wife Neilia and their one-year-old daughter Naomi were killed in a car crash. Their young sons Beau and Hunter were left badly injured.
Tragedy struck again in 2015 when Beau died of brain cancer, aged 46.
Biden also had to deal with the agony of Hunter's drug addiction and legal problems.
"Sometimes I marvel at Joe's strength. His life has been marked by cruel losses," First Lady Jill Biden, whom Biden married in 1977, said in her memoir "Where the Light Enters."
'President for all Americans'
With his family close around him, Biden did not let two failed presidential bids -- and a nearly fatal aneurysm in 1988 -- discourage him.
He served as Barack Obama's vice president for two terms, and his stubborn persistence in pursuit of the top job paid off when he came out of retirement to beat Trump in 2020, defying critics who said he was too old.
Saying at his inauguration he wanted to be a "president for all Americans," his old-fashioned centrism was a relief to many after the divisiveness of the Trump years.
At home he forced through a massive Covid recovery scheme and a green investment plan.
In Kamala Harris, his likely successor to the Democratic nomination, he appointed the first female, Black and South Asian vice president in US history.
US allies welcomed his pledge that "America is back" and his strong support for Ukraine.
But despite the best efforts of the White House to limit his public appearances, his age became the story again.
A series of senior moments culminated in the disastrous debate performance against Trump that doomed his bid for a second term.
As he fought to save it, he returned to the image of the underdog, often repeating his father's saying: "Don't compare me to the Almighty, compare me to the alternative."
Now Democrats have done just that.