I've read stuff saying that the American city went to Sh!t because of the manufacturing jobs were offshored in the 70s and 80s. Would tarriffs have helped?
Free trade is a net benefit for the country as a whole. The problem is that the benefits are widely distributed to the American consumers as a whole in terms of lower car prices, for example, but the costs are concentrated on steel workers whose jobs are outsourced. In theory some of the gains can just be redistributed to the economic losers as unemployment benefits and job retraining though a safety net and still leave society better off.
The laid off workers are much easier to see than the price of everyone's newest cars going down by $3000, so its easier for people to blame trade as a whole and advocate tariffs. America has a clunky, unresponsive welfare state so we get anti-system populists like Trump and Sanders.