Protectionism is not as simple a debate as the purists would like it to be. In theory, free trade is good, but consider steel as just one example:
Suppose the rest of the world modernizes their steel foundries, so that Chinese steel is not competitive, but China can subsidize steel workers for a lower net cost than they can support unemployed former steel workers. China then dumps this cheap steel on the global market to recoup some of the costs of subsidizing those workers to keep their jobs. Ignoring the quality issues with most Chinese steel, should we take advantage of the cheap Chinese steel, to lower consumer costs here, and accept the lost steel jobs in America?
I see some manufacturing jobs, particularly the low-end garment industry, as permanently gone, as they should be. I see other manufacturing jobs as recoverable, and some of those should be returned to the United States. Protectionism is a tricky question based on practical considerations and sometimes subtle details, not just abstract theory.
Some jobs should come back to the USA, and they will be more likely to if taxes are lowered to 15 percent and regulations are cut 75 percent, as Trump has said, and also if tariffs on imported inputs in USA manufacturing are not high.