always about trade offs, and balancing the consequences (higher, hopefully short term, costs, etc). But the question was hoo has the upper hand. He hoo controls the customer does, and that would be the U.S. in this particular example. We can buy elsewhere, pay a higher price, produce ourselves, or do without/with less. China cannot so easily replace us as their customer.

I would add the reverse would apply in the case of mostly inelastic items like energy, or monopolistic situations (doubly so if that's also virtually inelastic).