US President Joe Biden has wasted no time sharing his thoughts on Donald Trump’s bid for re-election, posting a slickly produced video on social media entitled Trump Failed America.

Mr Trump had confirmed the worst-kept secret in American politics less than an hour earlier when he told a partisan crowd at his Mar a Lago resort on Tuesday night (local time) he planned to again run for the presidency in 2024.

“Ladies and gentleman, America’s comeback starts right now,” he said to applause and cheers of “USA, USA”.

Mr Biden, who defeated then-president Trump for the White House in 2019, is in Bali for the G20 summit, and has been ensconced in an emergency meeting to discuss a deadly strike on NATO partner Poland overnight with a Russian-made missile.

But he broke into his schedule to make his terse response to the Trump announcement, along with an obviously pre-prepared video highlighting his Republican opponent’s perceived shortcomings.

Mr Biden has said he intends to run for re-election to a second four-year term in office, though he has yet to make a final decision.

Tweet from @JoeBiden

Great and glorious

Earlier at Mar a Lago, Mr Trump used a lengthy, often confusing address to outline why he wants to regain office.

“In order to make America great and glorious again. I am tonight announcing my candidacy for president of the United States,” he said.

“Three years ago when I left office … our nation was at the pinnacle of power and prestige. Striding into the future, confident and so strong,” he said.

“Everybody was thriving like never before.”

After rattling off a litany of his administration’s supposed achievements his speech at times veered into conspiracy theories and hit on many of the beats and topics popular with his followers.

Mr Trump, 76, painted a picture of a dystopian America under the 79-year-old President Biden, and prophesied the decline of the nation under the Democrat’s continued leadership.

“I am running because I believe the world has not yet seen the true glory of what this nation can be. We have not reached that pinnacle, believe it or not,” he told cheering fans.

Mr Trump hopes to beat potential Republican rivals and return his false claims of election fraud to the centre of US politics. Wednesday’s announcement follows a disappointing showing in last week’s midterm congressional elections that many Republicans blame on him.

The unusually early launch might well be aimed at fending off potential challengers for the party’s nomination in 2024, including rising star Florida Governor Ron DeSantis, 44, and Mr Trump’s own former vice president, Mike Pence, 63.

It came as Republicans closed in on the 218 seats they need to take a majority in the 435-seat House of Representatives.

• Inside Donald Trump’s ‘very big announcement’

Sources close to Mr Trump said he planned to push ahead despite mixed results from his endorsements this year, with losses by celebrity doctor Mehmet Oz in Pennsylvania and Don Bolduc in New Hampshire contributing to Republicans’ failure to win a majority in the US Senate.

Another Trump-picked candidate, former football star Herschel Walker, was forced into a December 6 runoff in his Georgia race against Democratic US Senator Raphael Warnock.

That has raised concerns Mr Trump’s announcement could again hurt Republican chances in a Georgia runoff, similar to the January 2021 runoff that gave Democrats their current majority.

Multiple Trump-aligned candidates who ran on platforms focused on his false claims of widespread election fraud were also defeated.

Conservative columnist Marc Thiessen urged him not to run again.

“That should be a wake-up call for Trump. He cannot win the presidency with his base alone,” Thiessen wrote in a Washington Post column.

“His conduct since losing office has made him unelectable.”

A Reuters/Ipsos poll taken before the midterm elections showed 53 per cent of Americans and almost one in four Republicans viewed Mr Trump unfavourably.

The poll showed a similar number of Americans viewed President Joe Biden unfavourably.

Investigations

Mr Trump will seek his party’s nomination even as he faces trouble on several fronts, including a criminal investigation into the removal of classified documents from the White House and a congressional subpoena related to his role in the January 6, 2021, US Capitol attack by his supporters.

Mr Trump has called the various investigations politically motivated and denies wrongdoing.

Mr Trump is seeking to become only the second US president in history to serve non-consecutive terms, after Grover Cleveland, whose second stint ended in 1897.

-with AAP