When many people think of the powerhouses of American international trade, they might think of the busy ports in Southern California or the financial hub in Manhattan. They probably don’t think primarily of a state like Indiana, but international trade benefits the interior of the country too — and tinkering with it through tariffs could upset those heartland economies that Washington always likes to talk about uplifting.

Despite ranking 17th in population, Indiana ranks eighth among states in the value of its exports to the rest of the world. Its $55 billion in exports equal 11 percent of the state’s GDP. ...