You're correct on that point, as well as every other point in your comment.
But here's an additional factor, one that is almost never discussed even by fervent advocates of an open international trading system:
Assume we have an omnipotent Emperor Trump. Could he ever force all Americans buy their textiles, clothing, shoes, toys, small appliances and consumer electronics exclusively from American factories? No, of course not. We simply don't have the labor force to do all such labor-intensive manufacturing.
What would it take to reach the Trumpian Utopia of an import-free American economy? One hundred million new workers? Two hundred million? We'd need massive immigration from third-world countries to do all that work. Moreover, we'd have to force native workers out of jobs in high-value manufacturing and services. No more aircraft factories. No more automobile assembly. No more technicians to repair computers and run fiber-optic cabling. Everybody put to work spinning textiles, sewing clothes, making toys and shoes.
But will the typical member of the Trump Brigades stop even for a few moments to ponder the contradictions inherent in their hero's disjointed ramblings on economic matters? Not a chance, my FRiend, not a chance.
Good question. Our newly-crowned emperor of really, really good, no, make that huge deals, no doubt in consultation with central_va and other assorted geniuses would make all of the necessary economic allocations, perfectly. After all, they know everything or can hire those Top Men who do.
They wouldn't need a mere 5-year plan, probably more like a 50-year plan.
So we could achieve "Juche," as the Norks call it, total self-reliance, an "original, brilliant and revolutionary contribution to national and international thought."
Or something like that. NO IMPORTS, baby! Imports are evil!
The Norks have annual GDP somewhere around 2K per capita. Nobody knows, that's just a guess, there being no published government figures. And who cares if half of them are starving and eat tree bark?
In the free-trading US, GDP per capita is about 55K. But, why stop there?
I'm sure we can drive that number down towards 2K if we exert enough protectionist effort. We, too, can eat tree bark if only we strive for Juche.