MANKATO — The presidential race’s tough talk on trade deals is cultivating worry among some farmers in Minnesota whose operations benefit from lower tariffs and primarily serve overseas customers.

Markets for Minnesota farmers have quadrupled in the 22 years since the North American Free Trade Agreement took effect, according to Kevin Paap, president of the Minnesota Farm Bureau, the state’s largest agricultural association.

Papp told MPR News that 95 percent of the industry’s customers don’t live in the U.S.

“We have to have trade in agriculture,” said Paap, who also farms near Mankato. “Whether it was NAFTA, whether it’s Trans-Pacific Partnership, we’ve got to be able to trade with the rest of the world.”

Republican presidential nominee Donald Trump has slammed the Trans-Pacific proposal, which would reduce trade barriers between North America and several nations across the Pacific, and he’s called NAFTA “one of the worst things that ever happened to the manufacturing industry.”

Democratic Hillary Clinton once praised the Trans-Pacific proposal but now opposes it, saying she supports global trade as long as it doesn’t hurt American workers.

University of Minnesota economics professor Robert Kudrle said blaming trade for economic problems in an easy campaign sell. But he said a country benefits overall from trade, even though it often hurts the pockets of workers in specific industries. He said focus should be on helping those workers, not punishing other countries that want to sell things in the U.S.

Kudrle said trade wars would damage not only agriculture and processed foods, which “are at the top of Minnesota exports,” but also the state’s sophisticated, high-tech manufacturers.