Washington (AFP) - US President Joe Biden will give an Oval Office speech Wednesday to explain his historic decision to drop out of the 2024 election and pass the torch to Kamala Harris, with the White House denying any cover up over his health.

In his first address to the nation since quitting the race, the 81-year-old is expected to burnish his legacy and deny he will spend six months as a lame duck president.

Armed with Biden’s endorsement, Vice President Harris has secured enough delegates to become the Democratic Party’s candidate in November to face Republican Donald Trump, and is already hitting the campaign trail.

“With your support, I am fighting for our nation’s future,” Harris said in a speech to a Black college sorority in Indianapolis.

She criticized Project 2025, a radical Trump-linked plan for government reform, as a bid to “return America to a dark past.”

Harris, 59, also paid tribute to Biden, saying that his speech at 8:00 pm (0000 GMT Thursday) would be about “not only the extraordinary work that he has accomplished, but about his work in the next six months.”

Biden stunned the world when he announced he would not seek reelection, bowing to weeks of pressure after a disastrous, stumbling debate performance against Trump last month.

The veteran Democrat will now use the powerfully symbolic setting of the Oval Office to try to restore some dignity as the clock ticks on his presidency and a half-century in public service.

White House Press Secretary Karine Jean-Pierre told reporters Wednesday that Biden’s decision has “nothing to do with his health.”

She denied that the White House had covered up any possible decline in Biden’s condition.

“It is not a cover up. I know that is the narrative that you all want. It is not,” she said.

- ‘Finish the job’ -

Biden said on X he would discuss “what lies ahead, and how I will finish the job for the American people” in the primetime televised speech.

He returned to the White House on Tuesday after spending nearly a week with Covid at his Delaware beach home, a period of isolation in which he took the decision to step back.

His speech comes just over a week since his last Oval Office address, following an assassination attempt on Trump on July 13. But it is only the fourth of his presidency overall – and could well be his last.

Republicans have called for Biden to step down altogether, saying that if he is not fit to stand for reelection then he is not fit to serve as president.

Jean-Pierre dismissed that as “ridiculous” and maintained that Biden is no “lame duck.”

The veteran Democrat insists he still has much to offer, with a particular focus on the economy and on disbursing money from a huge infrastructure bill for roads, bridges and airports.

He is also targeting a peace deal in the Middle East – a legacy-defining dream that many US presidents before Biden have chased.

- Netanyahu meeting -

Biden, who has been increasingly critical over Israel’s military campaign in Gaza, meets Israeli Prime Minister Benjamin Netanyahu at the White House on Thursday.

But in a sign of how quickly things are changing, Netanyahu will sit down separately that day with Harris.

Trump, meanwhile, said in a post on Truth Social that he will meet the Israeli leader Friday at the Republican’s Mar-a-Lago resort in Florida.

Biden’s decision to pull out upended a 2024 White House race that had threatened to become a sclerotic rematch between two elderly men.

It has injected a huge dose of enthusiasm into the Democratic Party after the turmoil over Biden, with Harris drawing exuberant crowds at her rallies.

Trump meanwhile has been forced to completely recalibrate a campaign which had revolved around bashing Biden’s age. The Republican himself is now the oldest candidate in US history.

He is due to appear in Charlotte later Wednesday for his first rally since Harris became the de facto nominee.

Polls underscore that the race remains very tight.

A CNN poll released Wednesday showed Trump with 49 percent against Harris’s 46 percent, within the survey’s margin of error, while also showing that Harris improved on Biden’s performance against Trump.