So the components are all imported from China, then assembled in Mexico. Maybe that's an improvement, and it keeps Chinese brands from establishing themselves, but does it really matter?
It doesn't keep Chinese brands from establishing themselves. As you noted, they'll build in Mexico and the US (See Volvo South Carolina, a Geely company, from China.) The brands will arrive in the US one way or another over the next 5 to 10 years and it will probably mean the end for non-trucks from domestic makers.
Well, Volvo had a presence in the US long before it became a Chinese subsidiary.
Of course some Chinese companies might try to penetrate the US market by manufacturing in North America, and that's already what a lot of foreign (but not Chinese) car companies do. Mazda, Toyota, BMW, etc all have factories in North America.
> levies will rise from 7.5% to 25% on lithium batteries, from zero to 25% on critical minerals, from 25% to 50% on solar cells, and from 25% to 50% on semiconductors.
> Tariffs on steel, aluminium and personal protective equipment – which range from zero to 7.5% – will rise to 25%.