Look at u.s. versus canada. Canada has been charging higher tariff on their exports than u.s., which means u.s. paying higher tax to canada for goods it purchases from canada. This money goes into their trade accounts, and this is why Trump says us is subsidizing canada. Of course this assumes inelastic demand, which means u.s. is going to buy their goods no matter what they charge. It can get more complicated that what i described.