> this can help some US company

These tariff threats are so broad. They are not aimed at encouraging this or that local industry. (And for the US you would need much more than a few percentage points of margin to encourage that.)

It feels like they are (1) threats. very crude threats. to get entire countries to change their policies a little this way or that - favoring the US a little more in exchange for dropping the threat. and (2) a source of govt revenue that doesn't look to the voters like income or capital gains tax. Although obviously it is - in the US everything ends up there.