President Trump on May 31 threatened to impose tariffs on Mexican imports. The Post's Nick Miroff explains the significance. (REF:AkhtarM/The Washington Post) President Trump’s plan to slap new tariffs on Mexican imports, weeks after escalating his trade war with China, leaves the United States fighting a multi-front campaign that threatens more instability for manufacturers, consumers and the global economy. The president’s bombshell announcement that he would impose 5 percent tariffs on Mexican imports, with the possibility of raising them to 25 percent if Mexico does not stop migrants fr...