VAN BUREN TOWNSHIP, Mich. >> President Joe Biden joined United Auto Workers strikers on their picket line today as their work stoppage against major carmakers hit day 12, a demonstration of support for organized labor apparently unparalleled in presidential history.

“You deserve the significant raise you need,” Biden said through a bullhorn while wearing a union baseball cap after arriving at a General Motors parts distribution warehouse located in a suburb west of Detroit.

He walked along the picket line, exchanging fist bumps with grinning workers.

He encouraged them to continue fighting for better wages despite concerns that a prolonged strike could damage the economy, saying “stick with it.”

He said “yes” when asked if UAW members deserved a 40% raise, one of the demands that the union has made.

“No deal, no wheels!” workers chanted as Biden arrived. “No pay, no parts!”

He was joined by UAW President Shawn Fain, who rode with him 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,” Fein said. “Not the CEOs.”

Labor historians say they cannot recall an instance when a sitting president has joined an ongoing strike, even during the tenures of the more ardent pro-union presidents such as Franklin Delano Roosevelt and Harry Truman. Theodore Roosevelt invited labor leaders alongside mine operators to the White House amid a historic coal strike in 1902, a decision that was seen at the time as a rare embrace of unions as Roosevelt tried to resolve the dispute.

Biden arrived one day before former President Donald Trump, the front-runner for the 2024 Republican nomination, goes to Detroit to hold his own event in an attempt to woo auto workers even though union leaders say he’s no ally.

Lawmakers often appear at strikes to show solidarity with unions, and Biden joined picket lines with casino workers in Las Vegas and auto 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 long wanted to stay out of the strike fray — until Biden.

“This is absolutely unprecedented. No president has ever walked a picket line before,” said Erik Loomis, a professor at the University of Rhode Island and an expert on U.S. labor history. Presidents historically “avoided direct participation in strikes. They saw themselves more as mediators. They did not see it as their place to directly intervene in a strike or in labor action.”

White House press secretary Karine Jean-Pierre told reporters aboard Air Force One en route to Michigan that “Biden is fighting to ensure that the cars of the future will be built in America by unionized American workers in good-paying jobs, instead of being built in China.”

Biden’s trip to join a picket line in the suburbs of Detroit is the most significant demonstration of his pro-union bona fides, a record that includes vocal support for unionization efforts at Amazon.com facilities and executive actions that promoted worker organizing. He also earned a joint endorsement of major unions earlier this year and has avoided southern California for high-dollar fundraisers amid the writers’ and actors’ strikes in Hollywood.

During the ongoing UAW strike, Biden has argued that the auto companies have not gone far enough, although White House officials have repeatedly declined to say whether the president endorses specific UAW demands such as a 40% hike in wages and full-time pay for a 32-hour work week.

“I think the UAW gave up an incredible amount back when the automobile industry was going under. They gave everything from their pensions on, and they saved the automobile industry,” Biden said Monday from the White House. He said workers should benefit from carmakers’ riches “now that the industry is roaring back.”

Biden and other Democrats are more aggressively touting the president’s pro-labor credentials at a time when Trump is trying to make inroads in critical swing states where unions remain influential, including Michigan and Pennsylvania. Biden is leaning on his union support at a time when labor enjoys broad support from the public, with 67% of Americans approving of labor unions in an August Gallup poll.

The United Farm Workers announced their endorsement of Biden today, calling him “an authentic champion for workers and their families, regardless of their race or national origin.” Biden’s campaign manager, Julie Chavez Rodriguez, is the granddaughter of Cesar Chavez, the union’s co-founder.

The UAW has not endorsed Biden. Asked about that after landing in Michigan, Biden told reporters that “I’m not worried about that.”

Trump is skipping the second Republican primary debate on Wednesday and will meet with striking autoworkers in Michigan, seeking to capitalize on discontent over the state of the economy and anger over the Biden administration’s push for more electric vehicles — a key component of its clean-energy agenda.

“If it wasn’t for President Trump, Joe Biden would be giving autoworkers the East Palestine treatment and saying that his schedule was too busy,” said Trump campaign adviser Jason Miller, referring to the small Ohio town that is still grappling with the aftermath of a February train derailment. Biden said he would visit the community but so far has not.

White House officials dismissed the notion that Trump forced their hand and noted that Biden was headed to Michigan at the request of UAW President Shawn Fain, who last week invited the sitting president to join the strikers.

“He is pro-UAW, he is pro-workers, that is this president,” White House press secretary Karine Jean-Pierre said Monday. “He stands by union workers, and he is going to stand with the men and women of the UAW.”

Yet the UAW strike, which expanded into 20 states last week, remains a dilemma for the Biden administration since a part of the workers’ grievances include concerns about a broader transition to electric vehicles. The shift away from gas-powered vehicles has worried some autoworkers because electric versions require fewer people to manufacture and there is no guarantee that factories that produce them will be unionized.

Carolyn Nippa, who was walking the picket line Monday at the GM parts warehouse in Van Buren Township, Michigan, was ambivalent about the president’s advocacy for electric vehicles, even as she said Biden was a better president than Trump for workers. She said it was “great that we have a president who wants to support local unions and the working class.”

“I know it’s the future. It’s the future of the car industry,” Nippa said of electric vehicles. “I’m hoping it doesn’t affect our jobs.”

Still, other pickets remained more skeptical about Biden’s visit today.

Dave Ellis, who stocks parts at the distribution center, said he’s happy Biden wants to show people he’s behind the middle class. But he said the visit is just about getting more votes.

“I don’t necessarily believe that it’s really about us,” said Ellis, who argued that Trump would be a better president for the middle class than Biden because Trump is a businessman.

The Biden administration has no formal role in the negotiations, and the White House pulled back a decision from the president earlier this month to send two key deputies to Michigan after determining it would be more productive for the advisers, Gene Sperling and acting Labor Secretary Julie Su, to monitor talks from Washington.

Krisher reported from Van Buren Township, Michigan. Associated Press writer Jill Colvin in Summerville, South Carolina, contributed to this report.