One of Donald Trump's talking points and biggest applause lines is how "they" -- Japan, China and Mexico -- are "beating us in trade" and are "taking our jobs." He proposes tariffs, for example, on Chinese goods in retaliation for that country's alleged "cheating." To someone who is out of work in an industry where foreign workers do what he or she once did, Trump-like protectionism sounds appealing. But Trump actually proposes punishing the American consumer. As economist Milton Friedman says, protectionism discriminates against low prices. It is certainly true that many countries prop up or subsidize companies or even...