The importer expends money, draining its economy, by producing things for itself it rebuilds its industries and economy, or it can simply find another source to import from.
The exporter has built its economy on selling things to the importer and can't easily replace the customer base, factories close and workers become unemployed, the money stops flowing and it can't pay for its expenses.
If the two countries are only a minor importer and a minor exporter the effect is diminished to the point that the principle falls within the margin of error and can fail.
But America is a large importer and China is an even larger exporter.
China has been allowed to have its cake and eat it too, and then eat everyone else's cake as well, if it tries to grab more it will fall out of the high chair and crack its skull on the tile floor.
And China is already losing its privileged position and many exports to other nations because it has already pushed things too far, mismanaged its centrally planned economy, and helped to destroy the economies of the countries that buy its imports.
The idea of China winning a trade war is laughable.
