President Trump makes every free market economist cringe when he boasts about getting agreement from other national leaders to purchase more American products, usually specifically referencing agricultural products. He insisted on soybean purchases being written into an agreement with Europe, has frequently spoke of Chinese commitments to purchase agricultural commodities and now he’s added Japan to his list of mercantilist deals.  In announcing an agreement in principle on a bilateral trade agreement, Mr. Trump is referenced in media reports as saying that Japan has agreed to buy “excess” U.S. corn. Japan already rivals Mexico for the position of being the number one buyer of U.S. corn and it is unclear what is mean...