Why did Joe Biden step down? Real reason President was urgently replaced by Kamala Harris

At the start of the year, pollsters anticipated a repeat of the 2020 contest between former President Donald Trump and a bitter battle between two men similar in age but antithetical in their outlook.

At the last election, Biden denied Trump a second term in office, with the former star of The Apprentice unseated following his administration's chaotic response to the pandemic and the economic crisis that followed.

Biden's tenure has returned to a more old-fashioned idea of the President, quietly governing largely without the drama that defined his predecessor's four years in the White House.

Biden, who served as Vice President under Barack Obama, had insisted that despite previous intimations during his first run for President, he would be a transitional figure he believed he was the right man to lead the country for another four years.

But by July, the Democrat, 81, had sensationally announced he would be dropping out of the race and endorsed his VP Kamala Harris for the Democratic nomination.

Harris quickly won enough support to replace him on the ticket. , she will face Donald Trump to decide who will become the figure still seen as the "Leader of the Free World."

But how did it all go so badly wrong for Biden? Here's all you need to know.

Biden, who grew up in a working-class Irish-American family in Scranton, Pennsylvania, has been in politics for over half his life. He was elected to the US Senate in 1972.

However, though he developed a reputation as an inspiring and effective communicator, harnessing the message of his rise from a blue-collar neighbourhood to the top of American politics, he also has a long history of verbal flubs and gaffes.

Biden was a household name when he ran for office, and his occasional mistakes seem to have been priced in among voters. However, during his presidency, concern grew among critics and, finally, even Democratic colleagues that his messaging was becoming more incoherent and his blunders more frequent.

At 81, Biden is the oldest President in American history. His uneasy traversal of the stairs onto Air Force One and mobility issues-including an embarrassing on-stage fall while handing out diplomas at a graduation ceremony in Colorado in June 2023-were constantly cited by Republicans as proof of his unfitness to serve and covered with relish in the conservative media.

He consistently resisted such concerns, acknowledging his age but noting that he is only three years older than Trump, 78, and asking to be judged on his record.

But after finally securing the top job after decades in Washington, Biden was forced to abandon his ambition of becoming a two-term President when his colleagues made clear his time was up.

Serious questions have been raised about Biden's mental acuity since his faltering debate performance in his first and last debate of the campaign against Trump in June.

During the face-off, Biden appeared to lose his train of thought on multiple occasions, prompting Trump to claim that he couldn't understand what the President was saying at one point.

Following the debate, political figures and pundits broached the idea of Biden being replaced as the Democratic presidential nominee.

David Axelrod, who had been a senior aide to President Obama, told CNN at the time: "There is a sense of shock at how he came out at the beginning of this debate, how his voice sounded. He seemed a little disoriented."

Other major verbal gaffes occurred in the weeks that followed, including him introducing during a summit before swiftly correcting himself.

Major figures in the Democratic party began joining Republicans in saying that Biden should drop out of the race, with Trump's lead over him widening.

Biden initially remained defiant but eventually bowed to colleagues' pressure and announced in July that he would "pass on the torch to the next generation."

Former House Speaker Nancy Pelosi was widely reported to have been an influential voice in the move to oust Biden following his disappointing debate performance, something Pelosi has stopped short of outright denying.

Announcing his decision on July 21, Biden explained that: "My mission has become clear to me. I need to unite my party in this critical endeavour."

"I believe my record as president, my leadership in the world, and my vision for America's future all merited a second term.

"But nothing, nothing, can come in the way of saving our So, I've decided the best way forward is to pass the torch to a new generation. It's the best way to unite our nation."

He continued: "I revere this office, but I love my country more.

"It's been the honour of my life to serve as your president. But in the defense of democracy, which is at stake, I think it's more important than any title."

Biden also announced his support for as the Democratic nominee, and by August 2, she had replaced him in the race after securing the backing of the 1,976 party delegates needed to get the nomination.