WAUSAU, Wis. — In China, ginseng is a popular gift prized for its healing powers, and surprisingly enough, Wisconsin-grown ginseng is considered the world’s best. In 2016,

590,000 pounds of the root, claimed to boost immunity and ease the effects of chemotherapy, was exported from the United States, most of it to China — with 98 percent coming from here in Marathon County.

But Mr. Trump’s trade war with China, along with the coronavirus pandemic, which has stymied air travel between the countries, has caused ginseng prices to plunge to 1970s levels, far below today’s production costs. Many farms, some of them generations old, are rapidly failing, according to Joe Heil, a longtime grower in Edgar, Wis., and a 20-year member of the Ginseng Board of Wisconsin.

In Marathon, Wisconsin’s largest county by area, voters traditionally lean Republican. 

Although Barack Obama won Marathon County in 2008, he lost it in 2012, and Mr. Trump enjoyed a sweeping win in 2016. 

For local Chinese-American ginseng farmers like Ming Tao Jiang of Hatley, the pain of the downturn has been worsened by Mr. Trump’s rhetoric blaming China for the virus.

Mr. Jiang and his wife, Feng Lu, a physician at Marshfield Clinic, “feel physically threatened for the first time in our lives,” he said. He has gotten stares, he said, and heard echoes of Mr. Trump’s references to the “Chinese virus” and “kung flu.” Mr. Jiang, who holds a Ph.D. in physiology, has worked to placate neighbors by giving away masks and ginseng. 

In Wausau, home to a large population of Hmong-Americans, residents have reported several racist attacks since the coronavirus outbreak, including being spat on, said Yee Leng Xiong, director of the city’s Hmong American Center. 

The heightened tensions, along with Mr. Trump’s immigration policies, have energized local Asian-American voters in this election, Mr. Xiong said, adding, “This is the most active and engaged I’ve ever seen them.” 

Throughout Wausau, competing Trump and Biden yard signs are evidence that Democrats are winning favor here. Along Highway 29, just outside Edgar, a dazzlingly bright LED billboard flashes “Trump,” but seconds later changes to a Biden ad. 

Trump flags fly over many farm fields, including Mr. Jiang’s, but he has no say, because, like many farmers here, he rents the property.

Because the Trump administration’s trade war hurt local dairy farmers as well, “I’m sure 5 to 10 percent of them are not so sure anymore” about their Republican allegiances, Mr. Jiang said. 

Mr. Jiang’s farm equipment still sports “Yang Gang” stickers in support of the former Democratic presidential candidate Andrew Yang, but he now hopes that Mr. Biden will win, fearing that Mr. Trump’s stubbornness could “boil over into war” with China.

“It started out as a business dispute,” he said. “Now it’s more ‘who’s the bigger guy on the block.’ It’s chilling.”

Mr. Heil, on the other hand, hopes Mr. Trump is re-elected and will play hardball with China until that nation backs down and rescinds tariffs as high as 41 percent on ginseng, or until U.S. tariffs on China’s exported ginseng match that level.

“We’ve always had to pay a tax and a duty to get ginseng into China — it’s never been a fair playing field for us,” he said. “Nobody will survive. There will be no ginseng industry in the U.S. if things don’t change soon. It’s sad.”