“The ag economy is not very good right now — fragile is the polite word for it,” Mr. Gould said.

His wife, Sandy, across the table, jumped in: “It’s in the tank is what he means.”

Mr. Gould continued, “So then when you go to great lengths to upset some of your key customers, there’s reason for concern.”

Three out of every five rows of soybeans planted in the United States find their way out of the country; half of those, valued at $14 billion in 2016, go to China alone. Mr. Gould estimates that 90 percent of his soybeans are exported, and 70 percent of his corn, so what he calls Mr. Trump’s “trade antics” — particularly his criticisms of Nafta — nag at him.

“It’s not only what happens today, but it’s the reputation of becoming an unreliable supplier,” he said.

Still, he’s not sure what will happen next, and he thinks that many farmers who supported the president are not yet ready to abandon him. “I think they’re going to wait and see how this thing plays out,” he said.

Farther north, in the tiny Wisconsin town of Dallas, where Andy Bensend grows soybeans on 5,000 acres, he is “guardedly optimistic” that the tariffs won’t spill over and hurt his business — even though his entire crop is meant to be shipped overseas.