Steel and aluminum may be the intended quarry of a trade war that President Trump has said would be “good” for the U.S. economy, but the casualties of the conflict could be food, agricultural economists warn.

China, the European Union, Mexico, Canada and other trading partners have sent strong signals that they may retaliate if Trump succeeds in imposing stiff tariffs on imports of steel and aluminum.

Each of those trading partners is a major buyer of U.S. agricultural goods, which amass a surplus of about $21 billion from worldwide trade, according to the U.S. Department of Agriculture.

“We could be in a really nasty trade spat, and we've seen that agriculture is usually a big target,” said Josh Rolph, manager of federal policy for the California Farm Bureau Federation. “We are greatly concerned.”

The wheat industry, which has pushed for more open international markets, blasted the proposal Friday. “It is dismaying that the voices of farmers and many other industries were ignored in favor of an industry that is already among the most protected in the country,” a joint statement from the National Assn. of Wheat Growers and U.S. Wheat Associates said.

Food frequently bears a steeper retaliatory penalty in trade wars. Agricultural products perish quickly, faster than politicians can argue. And while few people riot over the price of a smartphone, laptop or car, they've been known to overthrow governments over a food shortage or a spike in the price of staples.

No state has more at stake than California, which leads the country in agricultural revenue. Farmers and ranchers in the Golden State are twice as dependent on foreign trade as the country as a whole. World leaders also likely know that Trump enjoyed deep support in rural, agricultural areas, including much of the Central Valley, said Dan Sumner, an economist who directs of the Agricultural Issues Center at UC Davis.

Growers in California earned about $21 billion from trade, which amounted to about 44 percent of their total revenue in 2016, the last year for which full statistics were available.