US President Joe Biden has grabbed a bullhorn on the picket line and urged striking car workers to “stick with it” in an unparalleled show of support for organised labour by a modern president.

Donning a union baseball cap and exchanging fist bumps, Biden on Tuesday (local time) told United Auto Workers strikers that “you deserve the significant raise you need” as he stopped in the Detroit area.

His visit was just a day ahead of a planned visit by former president Donald Trump, the frontrunner for the Republican nomination in next year’s election.

“No deal, no wheels!” workers chanted as Biden arrived at a General Motors parts distribution warehouse, one of several facilities that has been targeted in a widening strike now in its 12th day.

“No pay, no parts!”

Despite concerns that a prolonged strike could undermine the economy, particularly in the crucial battleground state of Michigan, the Democratic president encouraged workers to keep fighting for better wages at a time when car companies have seen rising profits.

Asked if UAW members deserved a 40 per cent raise, one of their demands over the course of negotiations, Biden said: “Yes. I think they should be able to bargain for that.”

He has repeatedly argued that car manufacturers have not gone far enough to meet union demands, especially after the workers made concessions after the 2008 financial crisis hit.

“The fact of the matter is that you guys, the UAW, you saved the automobile industry back in 2008 … you made a lot of sacrifices. You gave up a lot. And the companies were in trouble. Now they’re doing incredibly well and guess what? You should be doing incredibly well.”

The White House said Biden was the first modern president to visit a picket line, a sign of how far he’s willing to go to cultivate union support as he runs for re-election.

Lawmakers often appear at strikes to show solidarity with unions, and Biden joined picket lines with casino workers in Las Vegas and car workers in Kansas City while seeking the 2020 Democratic presidential nomination.

But sitting presidents, who have to balance the rights of workers with disruptions to the economy, supply chains and other facets of everyday life, have stayed out of the strike fray – until Biden.

Unimpressed, Trump called Biden’s visit “nothing more than a PR stunt from Crooked Joe Biden to distract and gaslight the American people from his disastrous Bidenomics policies that have led to so much economic misery across the country”.

The president spent less than half an hour at the Willow Run parts distribution warehouse. He was joined by UAW President Shawn Fain, who rode with Biden in the presidential limousine to the picket line.

“Thank you, Mr President, for coming to stand up with us in our generation-defining moment,” said Fain, who described the union as engaged in a “kind of war” against “corporate greed.”

“We do the heavy lifting. We do the real work,” Fain said.

“Not the CEOs.”

Labour historians said they could not recall an instance when a sitting president had joined an ongoing strike, even during the tenures of ardent pro-union presidents such as Franklin Delano Roosevelt and Harry Truman.

Theodore Roosevelt invited labour leaders alongside mine operators to the White House during a historic coal strike in 1902. At the time, it was seen as a rare embrace of unions as Roosevelt tried to resolve the dispute.