Biden to give State of the Union speech as showdown with Trump looms

US President Joe Biden is preparing for perhaps the most crucial speech of his political career as the unpopular 81-year-old tries to convince doubters he is fit for a bruising rematch with Donald Trump in November.

With dominant performances in the "Super Tuesday" primaries and Trump's last Republican rival Nikki Haley finally dropping out, the two men have nailed down a clash that many American voters say they don't want.

But Democrat Biden will barely have time to breathe before Thursday's State of the Union speech to Congress, when he will seek to quell persistent voter concerns about his age and the economy.

The world will also be watching, with Israel's brutal attack on Gaza and the Ukraine War meaning the stakes of the November 5 election could hardly be higher for an increasingly volatile global order.

"You hired me to get the job done, build an economy that works for working people, and make life better for families," Biden wrote Wednesday on X.

"Tomorrow, I'll update you on our progress and lay out the path ahead."

The week of high American political theatre will set the scene for eight months of brutal campaigning as Biden tries to win a second term — and prevent Trump, 77, from making a historic White House comeback.

In an unprecedented scenario, Trump, who faces multiple criminal indictments — including over his attempt to overthrow the 2020 election — will face off against the oldest-ever president in US history.

'Historic achievements'

Within seconds of former UN ambassador Haley's withdrawal from the race on Wednesday, Trump and Biden were already scrambling to win over her moderate supporters for November's vote.

Trump invited Haley's supporters to "join the greatest movement in the history of our nation" — while Biden hailed her courage for telling the "truth about Trump" and said her fans had a place in his campaign.

Declining to endorse Trump, Haley said he would have to "earn the votes of those in our party and beyond it who did not support him."

Trump then leaned into the rematch with the man who beat him in 2020, saying on social media that he was ready to hold a presidential debate with Biden "ANYTIME, ANYWHERE, ANYPLACE!"

Health and mental acuity

But Biden must also physically convince voters that he's the man for the job, as he'll be in the public glare for at least an hour at a time when Trump has mocked his health and mental acuity.

For three days over the weekend , Biden huddled with close aides at the Camp David presidential retreat crafting the speech, which last year saw Biden brushing off heckling from Trump allies.

"Throughout today, and tomorrow, he's going to continue to fine tune the speech. This is something that he's personally involved in," White House Press Secretary Karine Jean-Pierre said on Wednesday.

Much of the speech could see Biden urging Republicans to end the political paralysis gripping Washington and pass key legislation, including on the Mexican border and aid for Ukraine.

Biden, however, has an uphill battle with voters despite posting clear wins on "Super Tuesday". Recent polls give Trump a narrow lead, with voters particularly concerned by Biden's age, and rating Trump better on the economy and immigration.

There are also warning signs from a protest vote over Biden's support for the Israeli war on Gaza.

"Biden could face a somewhat divided convention if he's not able to wrap up US involvement in the Israel-Gaza war," Todd Belt, a politics professor at George Washington University, told the AFP news agency.

Despite Trump's court cases, his continuing appeal among working-class, rural and white voters remained on display on "Super Tuesday."