Canada is Michigan’s biggest customer, but there's a growing tension between Canada and the U.S. The two countries are now taxing each other’s goods. In July, Detroit and Windsor were supposed to open a new bridge between them together. Canada canceled the joint ceremony and held its own.

The Supreme Court voided a big piece of these tariffs in February, and billions are flowing back —to the companies that paid at the border, not to the people who paid more at the dealership.

Jason Miller studies supply chains at Michigan State University. He joined host Robyn Vincent to follow the money, starting with a small metal loop on a car door.