You haven't thought this one thru have you.

Bring the jobs back to the US?  Modern plants are so highly automated that they employ a fraction of the workers the old ones did and the majority of those jobs are sufficiently high tech that they're not accessible to the majority of the people that worked at the "old" plant in any case.

But that's going to increase costs so the price of GM cars is going to go thru the roof - means a loss of market share so they'll have to employ even fewer people than you might have thought.

And of course the largest market for cars in the world is not the US - it would make more sense to get stuck with the duty on a small percentage of the cars they manufacture than it would to move the entire production to the US.

BTW - if he sticks imports with high duties does he actually think that the people on the other side of that trade agreement won't retaliate?  That's pretty much the end of the US export business (and the associated jobs).  Not just cars.