Belleville (United States) (AFP) - Joe Biden became the first sitting US president to stand on a picket line Tuesday, joining striking auto workers in Michigan in a bold pitch for blue collar votes against likely election rival Donald Trump.

Wearing a United Auto Workers (UAW) union baseball cap, the Democrat used a bullhorn to tell red-shirted employees they deserved “a hell of a lot more than what you’re getting.”

His short but symbolic trip came a day before Republican former president Trump visits Michigan, the historic heart of the US car industry and a key battleground for the 2024 election campaign.

“They’re doing incredibly well and guess what, you should be doing incredibly well too,” Biden said to cheers from placard-waving union members.

Sporting a blue zip-up top with a presidential seal, Biden urged automakers Ford, General Motors and Stellantis to “step up for us.”

Biden then shook hands with union workers, closely watched by Secret Service agents, and agreed when asked if employees should get a 40 percent increase.

“It meant a lot,” said Carolyn Nippa, 51, an inventory control employee at the GM plant after she fist-bumped the US president.

“It’s very historic.”

- ‘Stand up with workers’ -

The autoworkers strike that began on September 15 has increasingly become a political football for Biden and Trump as they head for a probable rematch next year.

Biden’s trip was designed to trumpet his pro-union credentials amid growing concerns about his poll ratings, his age and his struggles to get his economic message across.

The White House played up the historic element, with Press Secretary Karine Jean-Pierre stressing it was the “first time a sitting president has visited a picket line in modern times.”

Biden’s trip also went down well with unions, whose support was crucial when he beat Trump in 2020.

The UAW’s outspoken chief Shawn Fain, who invited Biden to Detroit, greeted him on the tarmac and rode with him to the picket line in the presidential limousine dubbed “The Beast.”

“Our president chose to stand up with workers,” Fain, whose union is pushing the car makers for better pay and conditions, told the crowd.

Trump meanwhile is hoping to woo back working-class voters, who propelled the right-wing populist to the White House in 2016 on the back of his promise to restore American industry, but then largely flipped to Biden.

The wealthy property tycoon’s own links with the unions are more difficult, and the car parts plant Trump is visiting on the other side of Detroit on Wednesday is non-union.

“We would not consider that standing in solidarity if you are going to a non-union shop while a strike is going on,” said a UAW source.

- ‘Stick with it’ -

Instead, Trump has focused on attacking what he called Biden’s “draconian” push to fund a shift to more environmentally friendly electric vehicles, saying it is driving jobs to China.

“Crooked Joe should be ashamed to show his face before these hardworking Americans he is stabbing in the back,” the 77-year-old said in a statement Tuesday, using his usual epithet for the president.

Trump, who’s skipping a Republican candidates’ debate on Wednesday to focus on Michigan instead, also accused Biden of copying his plans to visit the state.

Biden says his push on electric vehicles is part of a plan to bring manufacturing jobs back to the United States and lead a global race to develop green technology.

For all that, his “Bidenomics” message is failing to get through to voters.

An ABC News-Washington Post poll sent shivers up Democrats’ spines on Sunday when it showed Trump beating Biden 52 percent to 42 percent in a head-to-head match-up.

And while other polls have put them roughly even, Biden’s approval ratings remain stubbornly low, particularly on the economy where high prices are blotting out good jobs numbers.

But Biden’s message to doubters appears to be the same as it was to the striking workers in Michigan: “Folks, stick with it.”