Re: Good for Trump
Reality probably lies somewhere in between. Were it so interchangeable to move wholesale, most of the companies most likely would have done so. Those that are in the US appear to have some reason to do so. Would shutting down the supply be a nudge towards leaving? Yes. Would it force all to? Of course not. Footprint sizes may change geography, but none of us can do much more than theorize to what extent.
There's a balance to be reached and I'm not suggesting we close down all immigration, but using the visa system as a way to discriminate against and cause domestic workers lose interest in supposedly critical fields is not going to bode well for the US in the long.