the reasons trump is doing this don't have anything to do with workers; one might rather note trump's treatment of south korea as a chinese satellite with a level of alarm. but, it could very well provide incentives for korean and chinese businesses to manufacture more goods in the united states, which would indeed import some jobs from elsewhere into the united states. but, at what retaliatory cost is unclear.

i don't have any particular aversion to tariffs in principle, it's more that using them is a really tricky game that requires quite a bit of mathematical analysis and intelligent foresight - qualities the president does not have. tariffs should certainly not be used haphazardly as a hegemonic tool of control, but that box is already long open.

http://www.bbc.com/news/business-42784380