Given Iowa’s dependence on global trade, its economy offers a test case for understanding the hypothetical impacts of a trade war like the one President Donald Trump seems to want. In early March, Trump announced tariffs on aluminum and steel, with China intended as a prime target. Then on March 22, following an investigation into Chinese trade practices and intellectual property theft, Trump proposed levying tariffs on more than $50-billion-worth of Chinese goods. Yesterday, China began levying a 25 percent tariff on eight U.S. products, including pork, along with lesser tariffs on 120 other goods, in retaliation for the duties on aluminum and steel. Retaliatory tariffs for Trump’s intellectual property theft actions could follow, Xinhua hinted. China has “yet to unsheathe its sword” in that area, the news agency reported. The Trump administration’s list of tariffed products is due on April 6.

To understand the broader logic behind Trump’s belligerent stance on trade with China, it’s important to know that, in most sectors, the United States imports far more from China than it exports. “Putting America First,” Trump believes, means imposing tariffs to disrupt that trade deficit. As Trump t weeted on March 2, in a thinly veiled reference to China, “[W]hen we are down $100 billion with a certain country and they get cute, don’t trade anymore—we win big. It’s easy!” (The actual annual trade deficit with China in 2017 was $375 billion.)

But in a few select sectors, America has a trade surplus with China. Two categories routinely top the list: aircrafts, and soybeans, grains, and seeds. Other agricultural products like pork are crucial exports as well. Because Iowa’s hog operations are located near the cornfields that are used for feed, it is actually cheaper to produce pork there than in many parts of China. The country also buys a host of products that are not in great demand elsewhere, like pork intestines. A proposed 25 percent tariff on U.S. pork would mean a loss for farmers of up to $7 per hog, according to agricultural economist Chris Hurt.

Beijing has dangled the possibility of a tariff on soybeans as well. In 2016, the Peterson Institute for International Economics modeled the possible impacts of Chinese restrictions on soybeans. Some American counties could suffer job losses as high as 40 percent, the Institute found.

Chinese leaders are fully aware of Trump’s dependence on the heartland for political support. In a video recently posted on the website of the state-owned newspaper Global Times, the paper’s editor boasted about the country’s capacity to hit Trump where it hurts by taxing U.S. soybeans. “You cut flesh from me,” he said, “and I’ll make sure to knock out your front tooth.”

Iowa is, in fact, critical to the U.S.-China relationship. In 1985, Xi, then the deputy party secretary for a county in Hebei province near Beijing, joined a Chinese agricultural delegation to the state. He stayed with a couple in Muscatine, a farming community of 20,000 people, sleeping in their son’s bedroom, whose walls were covered in football-themed wallpaper. While there, he befriended future Governor Terry Branstad. On his 2012 visit, Xi returned to rural Iowa as China’s vice president. At a 400-acre farm outside Des Moines, he braved the February cold to pause for a photo op atop a John Deere tractor—another Iowa export—as Branstad looked on approvingly. (A full-scale replica of the farm Xi visited is now under construction in Hebei.) In 2016, when Trump announced that he was appointing Branstad ambassador to China, he joked about the governor’s longstanding ties with the country. During the campaign, Trump recalled, “He always would say, ‘Mr. Trump, Donald, don’t say anything bad about China when you’re in Iowa.’”

Not all farmers would agree that China is beyond criticism. Over the past two years, I made several trips to Iowa to talk to farmers about their relationship to China. Profits from export-driven agriculture have largely gone to agribusiness companies like Cargill, and resentment among farmers is running high. The U.S. Department of Agriculture recently predicted that in 2018, U.S. farm incomes will sink to a 12-year low. The economic unrest generated by such plummeting fortunes helped fuel support for both Trump and anti-China sentiment. (I met some enterprising farmers who were studying Chinese. Others had trouble discussing the country without resorting to racist epithets.)