Republican U.S. presidential candidate Donald Trump on Sunday said he would slap tariffs as high as 200% on vehicles imported from Mexico as he ratchets up his protectionist trade rhetoric ahead of the Nov. 5 election.

Trump, facing Democrat Kamala Harris in a tight race, has previously pledged that if elected again as president he would set a 100% duty on imported cars and trucks with the goal of aiding the domestic auto industry. But while speaking at a rally at an airport in Juneau, Wisconsin, Trump doubled the figure.

"We'll put a tariff of 200% on if we have to," Trump said. "We're not going to let it happen. We're not letting those cars come into the United States."

The former president stumped in Wisconsin for the fourth time in eight days, underscoring the importance his campaign is placing on the state with less than a month to go until Election Day.

Opinion polls have shown Harris, the U.S. vice president, with a slight edge in Wisconsin after the state voted for President Joe Biden over Trump four years ago.

Both Harris and Trump have expended a massive amount of time, money and resources in Michigan, Pennsylvania and Wisconsin, which are considered keys to victory in the U.S. electoral college. Trump swept the states in 2016 against Democrat Hillary Clinton on his way to becoming president. Biden did the same in 2020.

Harris campaigned with former Republican U.S. congresswoman Liz Cheney in Wisconsin on Thursday.

Trump's rally in Juneau came less than 24 hours after he staged a rally in Butler, Pennsylvania, the site of an assassination attempt against him in July.

Trump made his remarks on tariffs as he pledged to bolster the U.S. auto industry. Experts have said his plans could increase vehicle prices.

Mexico exported about 3 million vehicles to the United States in 2023, with the Detroit Three automakers accounting for about half of those exports.

The Tax Policy Center think tank has said that a massive new tariff on Mexican vehicle exports "likely would drive up the cost of motor vehicles, domestic as well as imports, used cars as well as new."

Trump previously threatened large tariffs on cars from Mexico as president and as a candidate in 2016. Imposing up to 25% tariffs on Mexican autos and components could have severe impacts on the industry and hike vehicle costs, automakers said in 2019.

Trump spent much of the early part of his nearly two-hour speech in Juneau bashing the Biden administration's response to Hurricane Helene, which devastated parts of the Southeast and left 227 people dead and hundreds of thousands without power.

Harris had left people "stranded," Trump said, without providing evidence.

"This is the worst response to a storm or a catastrophe or a hurricane that we've ever seen," Trump told the crowd in Juneau.

Earlier on Sunday, Deanne Criswell, the administrator of the Federal Emergency Management Agency, on ABC's "This Week" program defended the administration's actions, saying that the agency has enough resources to aid in recovery efforts.

"We continue to move in critical commodities into the places that have been hard to reach," Criswell said.

Criswell called claims by Trump and other Republicans that FEMA funding was being diverted to migrants in the country illegally "frankly ridiculous and just plain false."