Earlier quoted context omitted.
America First and protectionism is how Trump won Michigan, not how he won the Republican primary (and thus Mississippi, Georgia, Texas, etc.) He got nominated by being the candidate most resembling a middle finger to the establishment. The existing system has been systematically destroying the middle class, and the people see it happening but don't understand why or how to fix it, but they know that voting for establ…
I honestly don't think he has promised anything to address the points you raised, or has any intention to.
Nobody knows what Trump will do. Make America Great Again could mean anything. Compare "Hope and Change" -- Obama was the first attempt at this when he defeated Clinton. Change didn't happen so people chose an even more radical option.
It isn't that voting for the protest candidate is especially effective, it's that frustrated people don't know what else to do. They weren't given any good option so they picked the wildcard bad option over the known bad option.