By Cokie Roberts and Steven V. Roberts

The president has triggered a trade war with China, and the bombs are falling on his own allies in the Farm Belt.

Donald Trump’s decision to impose tariffs on imported steel and aluminum, plus $50 billion in additional products, has provoked two waves of retaliation by China against American farmers who export pork, beef, soybeans and sorghum. The Wall Street Journal reports those measures are deliberately aimed at hurting Trump’s base, and they are succeeding.

The Brookings Institution calculated the impact of China’s initial sanctions against farm products (except for wine, a geographical anomaly): 65 percent of the affected workers live in counties carried by Trump.

Sen. Pat Roberts, a Kansas Republican who chairs the Agriculture Committee, sputtered in anger when asked about the effects of the president’s actions. “These are the people who voted for the president,” complained Roberts. “These are his people. One county in Kansas even voted for him 90 percent, and they’re not going to be happy at all about this.”

With global prices dropping and competition rising, notes Zippy Duvall, president of the American Farm Bureau Federation, “This could not be happening at a worse time for American agriculture.”

The trade war is not the only way Trump’s policies are punishing agriculture. The president’s crackdown on immigration — from lowering refugee quotas to accelerating the deportation of undocumented workers — has already been shrinking the supply of workers willing to pick crops, pluck poultry and pack meat.

A year ago, Duvall told the Financial Times that “half or more of farm workers in some areas are undocumented immigrants and (their) members have already begun to report shortages.”

The president’s tariff tantrum is part of a wider pattern of protectionism. He’s already pulled out of the Trans-Pacific Partnership negotiated by his predecessor and repeatedly threatens to “terminate” NAFTA, the North American Free Trade Agreement, which he labels “the worst trade deal ever made.”

The farm sector is alarmed because it is so export-oriented. The Farm Bureau Federation calculates that $135.5 billion worth of agricultural goods were sent abroad in 2016, or about one-quarter of total farm output. But for some products, the rate of exports is much higher. For cotton, the figure is over 75 percent; rice is over 50 percent; soybeans are just under 50 percent.

“American farmers appear to be the first casualties of an escalating trade war,” former Democratic Sen. Max Baucus, chairman of Farmers for Free Trade, said in The New York Times. “With farm incomes already declining, farmers rely on export markets to stay above water. These new tariffs are a drag on their ability to make ends meet.”

Hog farmers alone sent more than $1 billion worth of pork to China last year. Jim Monroe, spokesman for the National Pork Producers Council, told The Wall Street Journal: “Exports are the lifeblood of the industry.”

When exports decline, it’s not just farmers who suffer. Packers and truckers, dockworkers and merchant mariners, seed and equipment dealers — they all take a hit, too.

If exports are the lifeblood of agriculture, then immigrant workers are the muscle and sinew. The Times profiled a labor recruiter, Ray Wiley, who says “employers call us all the time” begging for workers to staff their processing plants, and foreigners are virtually their only source of labor.

“They want the American dream, and they don’t mind starting off at the bottom,” Wiley says of those immigrant workers, both legal and illegal. “There’s a lot of unskilled work in the U.S. that Americans will not do, and these people are doing it.”

And they’re doing it in places that voted heavily for Trump. Take, for instance, the Texas town of Cactus, where a Washington Post reporter describes the workforce at a local meat packer that sells hamburger to Burger King and steaks to Walmart. Cactus is in Moore County, which voted 75.5 percent for Trump.

“There are Burmese meat cutters a few years removed from refugee camps in Thailand and Malaysia,” writes reporter Nick Miroff. “Chuckers from Sudan, tall and strong, who specialize in separating the spinal cord from the side of beef swinging on a moving chain. Somalis who showed up in such numbers that Moore County at one point had the fifth-highest per-capita Muslim population in the United States.”

Farm country like Moore County helped elect Trump the first time. Will those voters support him again if his trade and immigration policies continue to jeopardize their economic future?

Steve and Cokie Roberts can be contacted at stevecokie@gmail.com.