In the wake of the unfolding events in Afghanistan and doubts in Asia about the durability of American commitments, the United States should rejoin the Trans-Pacific Partnership. Trade allows nations to specialize in what they do best. Value-added per employment is about 11% greater in U.S. export industries than import-competing activities; consequently, specialization adds about $280 billion annually to the gross domestic product. U.S. exporters spend more on research and development and creative intellectual property than other businesses. Wider global markets permit Apple, Intel, Disney and Netflix to invest more in new products and more fundamental research. Exports allow larger...