President Joe Biden addressed striking auto workers on the picket line in Michigan on Tuesday, speaking through a bullhorn while flanked by union leaders.

Biden said he backed the striking workers’ demands for a 40% pay increase over the next four years. They are also asking for full-time pay for a 32-hour workweek.

“Companies were in trouble, now they’re doing incredibly well. And guess what? You should be doing incredibly well, too,” he said.

The president of the United Auto Workers, Sean Fain, greeted Biden when he arrived in Michigan.

“This is a historic moment — the first time in our country’s history that a sitting U.S.A president has came (sic) out and stood on the picket line,” Fain said.

Unions and unionized workers are a key constituency of Biden’s. They give him and other Democrats millions of dollars in donations, and they also help turn out Democratic voters. But the UAW has not endorsed him yet for 2024.

Auto workers are on Day 12 of strikes, shutting down General Motors, Ford and Stellantis plants.

Auto workers strike will likely expand Friday

“This is absolutely unprecedented. No president has ever walked a picket line before,” Erik Loomis, a professor at the University of Rhode Island and an expert on U.S. labor history, told The Associated Press. 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.”

Biden announced his visit to Detroit after 2024 presidential front-runner Donald Trump said he would skip the second Republican primary debate and instead travel to Michigan to meet with auto workers.

Trump is expected to speak to workers at Drake Enterprises, an auto supplier in a Detroit suburb that is not unionized.

On Tuesday, Trump criticized Biden over his administration’s requirement that auto makers shift to producing electric vehicles. The administration is spending billions to support its goal of having 50% of cars sold be electric vehicles.

In a statement, Trump said Biden’s “electric vehicle mandate will annihilate the U.S. auto industry and cost countless thousands of autoworkers their jobs.”