US manufacturers are fine because the US has a long history of economic protectionism. These cars are effectively banned in the US due to tariffs which protect US automakers.
More importantly, the US will ban Chinese automation tech. Which is just fine by me. But I drive a 10 year old car.
Tariffs alone can't keep out cheap foreign products.
Aren't you missing something? Gemini tells me that non-NA market makes up 33% of Ford's sales, and 51% of GMs.
So a better way to put it is "protects US automakers in the US." And that assumes NA manufacturers would be unaffected by declining sales abroad.