Here's the economist line on Trade.
Al wants to trade with Jill.
Al grows corn, Jill builds cars.
Since Al has more corn than he needs, and Jill has more cars than she needs, the trade makes both Al and Jill happier.
If Al grows corn, and both Jill and George make cars...if Jill makes cars better than than George (cheaper or higher quality), then Al will trade with Jill.
Protectionism is when George convinces his Uncle to threaten (anonymously) to beat Al senseless if he trades with Jill. Then Al buys from George, is less happy than he would have been, Jill is less happy than she would have been...maybe Al doesn't buy at all, because it's not worth the trade....but most likely, we've transfered a lot of value away from Jill (no corn), a little value away from Al, and a medium amount of value to George.
Clearly, in the first place, Uncle is immoral, and clearly the net benefit to everyone has gone down substantially. Unsurprisingly, this kind of thing only happens when George convinces his Uncle to threaten folks. It's bad for Al, bad for Jill, and good ONLY for George.
If Mechanic Mike went out and built a machine that transformed corn into cars...then George convinced his Uncle to smash the machine...it would be EXACTLY the same situation.
George uses thuggery to prevent Al and Jill who want to trade from doing so. George gets rich off his thuggery. Al and Jill or Mike are worse off. It's questionable whether the net benefit to George is higher than the net loss to Al. It is obvious that Uncle has net-destroyed significant value once everyone is taken into account...though if you have some way of counting Jill/Mike as somehow unimportant, then you can edit your calculus substantially.
Protectionism is preventing (with violence) Al and Jill from trading IN ORDER TO make a George richer and the other two poorer. Nothing more, nothing less. Frequently it even works.
Money flows, as always from the poor and weak to rich, politically connected confabulists who can spin myths that explain why their interest is "good for the country".