One can understand why President Trump thinks trade terms with other countries is like what he has done, negotiating a private deals. If the other partner is in a weaker position one can take advantage. Trade is different.
While trade in economics is explained by the theory of comparative advantage, there is a simpler way. Tariffs hurt both countries. Think of having tariffs between our states. So far as I know, no country in the world allows states or provinces to charge tariffs for goods passing from one to another. Tariffs on goods passing from ND to MN would harm sides of the Red River.
Our Constitution came about because the 13 colonies were charging tariffs at their borders. George Washington and some others could see the harm and called for the famous Constitutional Convention in 1779 to stop it.
The link discusses an article in the New York Times today about North Dakota. The reporter interviewed farmers and politicians in ND for their reaction to Trump’s tariffs. Farm prices, especially soybeans and pork bought by China, have fallen. China reacted to Trump by putting import tariffs on those two products. Chinese leaders knew exactly how to harm Trump.
Trump is trying to help our less efficient industries, aluminum and steel, and he has hurt those most efficient, soybeans and pork. It is harder for U.S. consumers to buy things China can make more cheaply than we can.
The Times reporter concluded farmers will support Heitkamp and turn against Trump if he runs again.