President Trump is calling for a “pro-America trade policy,” meaning a return of tariffs that will protect domestic industry. The idea has a venerable pedigree, Trump noted, pointing to President McKinley, who reckoned that tariffs had made American life “sweeter and brighter.” Sages as far back as Hamilton have backed nurturing native industry behind a tariff wall. Yet the last time we experimented with a tariff shield, the results were disappointing.