Through trade pacts and institutions like the World Trade Organization, the United States has sought to rip down barriers to global commerce, including quotas and taxes on imports. Imports cut prices for consumers, and exposure to foreign competition makes American firms and the overall U.S. economy more efficient. [...] critics charge that China doesn't play by the rules — unfairly subsidizing exporters, manipulating its currency to give them a competitive edge and condoning the theft of U.S.