Biden, 80, announces 2024 re-election bid

US President Joe Biden announced Tuesday he will seek re-election in 2024 and "finish the job," plunging at the record age of 80 into a ferocious campaign that could set up a rematch against Donald Trump.

Launching his pitch in a video on the fourth anniversary of the day he began his 2020 challenge against Trump, Biden said he was still fighting to save American democracy from Republican "extremists."

"When I ran for president four years ago, I said we're in a battle for the soul of America. And we still are," Biden pronounced in the voiceover.

"That's been the work of my first term: to fight for our democracy," Biden said. "Let's finish this job."

After a series of big domestic legislative wins and momentous foreign policy struggles, including leadership of the Western coalition helping Ukraine resist Russian invasion, Biden has no real challenger from within the Democratic Party.

Another big boost is a powerful post-pandemic US economic recovery, helped by historic federal spending to renew infrastructure and encourage investment in the high-tech electric vehicle and semiconductor sectors.

"That's what we're doing: rebuilding America," Biden told a crowd of cheering trade union workers at a Washington hotel conference room later Tuesday, in his first speech since launching his re-election campaign.

Biden cast himself as champion of blue collar Americans and said Republicans cared more about Wall Street.

"I think there should be a minimum tax for billionaires," he said in the speech, interrupted by extended applause and a chant of "four more years!"

"No billionaire should be paying a lower tax rate than a construction worker, a school teacher, a firefighter, a cop, a nurse. I mean it, it's simply wrong," he said.

Biden was fired up, but he will face constant and fierce scrutiny over his age.

He would be 86 by the end of a second term. Even if a medical exam in February found him "fit" to execute the duties of the presidency, many including in his own voter base believe he is too old.