Former President Donald Trump on Saturday vowed to make the auto industry “bigger and better” than ever, hoping to score votes with car workers in battleground Michigan. 

Mr. Trump’s rally in Novi, a suburb of Detroit, came as early voting in Michigan kicked off and with just 10 days until the Nov. 5 election.

But his recent remarks that auto assembly line work could be done by a child earned him heat from the United Auto Workers.

The former president acknowledged that he received backlash for his comments recently at the Economic Club of Chicago but doubled down that the Motor City “needs help.” 

“I’ve been hearing about promises for 40 years [regarding] Detroit,” he said. “We’re going to make the promise you can have those car companies come roaring back through intelligent uses of tariffs, taxes, incentives. … If they don’t come back, they’re not going to be selling any cars in this country, let me tell you right now.”

Mr. Trump touted his move to dissolve the North American Free Trade Agreement, which he said ate away at jobs in the auto industry, and replace it with the United States-Mexico-Canada Agreement and vowed to build more car factories in the country. 

He would attract more auto jobs back to the country, in part, by reducing the corporate income tax rate from 21% to 15% for companies that produce products in America, and through tariffs. 

“If they want to partake in this market, we’re going to make it the greatest market in the world, then they’re going to have to pay a price, and the price is either a stiff tariff or you don’t have to pay the tariff, you’ll build the plant in the United States that you people are going to run,” he said. 

Michigan has 8.4 million registered voters and 15 Electoral College votes up for grabs and is one the seven battleground states where the Trump and Harris campaigns have spent the bulk of their time.

Later on Saturday, Ms. Harris was to hold a rally with Michelle Obama in Kalamazoo, Michigan, marking the former first lady’s first appearance on the campaign trail this election cycle. 

Democrats are hanging their White House ambitions on Blue Wall states, like Michigan, Wisconsin and Pennsylvania, which propelled the past two Democratic presidents to Pennsylvania Avenue. 

Mr. Trump and Ms. Harris have traded thin leads in Michigan since the vice president entered the race this past summer. As of Saturday, the former president led by less than a quarter of a point, according to RealClearPolling. 

The latest poll of the Michigan race from Quinnipiac College had Ms. Harris leading Mr. Trump by 4 points. Despite his pitch, Ms. Harris leads with auto union workers. 

This week, the UAW released a poll showing rank and file members tended to favor Ms. Harris over Mr. Trump in swing states by 22 points. In Michigan, UAW members favored Ms. Harris by 20 points.

 “The candidates’ track records speak for themselves. Harris has been in our corner in tough fights. Trump’s been a scab who passed NAFTA 2.0 and wants to bust unions,” UAW President Shawn Fain said in a statement. “When you break it down like that and reach members in one-on-one conversations, the choice for president becomes clear.” 

But the former president could get support from Michigan’s Arab American voters, who are split on whether to support Ms. Harris because of the Biden administration’s policies in the Israel-Hamas war. 

“If the Muslim and Arab community gets out the vote, that’s one more reason that Donald Trump is going to win Michigan,” said former Trump White House adviser Stephen Miller.

Mr. Trump, who said he would “set an all-time record with the Arab and Muslim voters” in the state, scored an endorsement from Hamtramck Mayor Amer Ghalib, the first Muslim and Arab American to govern the locale.