US President Joe Biden donned the signature red T-shirt of America's biggest car workers union and lashed out at Donald Trump Thursday as he tried to fire up their support for his 2024 reelection bid.

"Donald Trump often says we're now a failing nation," the 80-year-old Democrat told workers in Illinois who recently won pay hikes and the reopening of a factory after weeks of strikes. 

"That's not what I see. I know what we can do if folks are given half a chance." 

Some of the United Auto Workers (UAW) members in the crowd shouted "Jail Trump" as Biden lashed out at the scandal-tinged Republican former president, whom he beat in 2020.

Biden is trying to jumpstart his reelection campaign after a series of polls showed him trailing Trump in a likely rematch next year, despite his rival facing a string of criminal trials.

Recent polls have shown voters have particular concerns about Biden's age, but he gave an energetic turn to the audience filled with jokes and pops at Trump. 

- 'The Other Guy' -

A local union chief helped him put the crimson UAW T-shirt over his collared shirt, as he came to celebrate the news that automaker Stellantis would reopen the plant it had closed in Belvidere in March as part of a deal to end the strikes.

Trump and Biden are both trying to win blue-collar votes in swing states, with the two men making rival visits to the historic car-making state of Michigan in September and Biden throwing his weight behind the unions.

Biden lambasted Trump for failing to visit union members back then when they were striking against the "Big Three" US automakers, Ford, General Motors and Stellantis.

"Remember the other guy?" Biden said, referring to Trump. "I stood with you shoulder-to-shoulder, my predecessor went to a non-union shop and attacked you."  

Biden also hit out at Trump for failing to back the transition to electric vehicles, which the Democrat has made a key plank of his policy to rebuild American manufacturing by promoting green technology.

"Like almost everything else he said he was wrong, and you have proved him wrong," said Biden.

French-Italian-US automaker Stellantis idled the plant in March of this year but is now reopening it and bringing back more than the 1,200 jobs, on higher wages, the White House said.

The firm is also investing in battery making for electric vehicles which will create a further 1,000 jobs.

- 'I'm beating him' -

Biden was introduced on stage by the powerful head of the UAW, Shawn Fain. 

A long-term union supporter who became the first US president to visit a picket line in Michigan in September, Biden appeared to relish UAW's backing on Thursday.

He joked about his age -- "I know I only look like I'm 30 but I've been around for a long time". And when a reporter tripped in the media area he said "I just want the press to know that wasn't me", referring to a number of incidents when he has fallen.

Biden then returned to the theme that he has tried to drum home with US voters -- so far without success, according to opinion polls -- that under his watch the US economy is booming and that he backs workers.

"These deals are a game changer, not only for UAW workers but for all autoworkers in America," he told the union members.

Before leaving the White House, Biden had also rejected the recent polls that showed him trailing Trump in five key swing states, and leading in only one.

"Ten polls -- eight of them, I'm beating him in those states. You guys only do two," he told a reporter who asked him about the surveys.

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