Democrats in farm states are busily warning their rural neighbors that President Trump betrayed them with his tariff pressures, which may especially impact U.S. farm exports to China. China has imposed a 25 percent tariff on U.S. soybeans, wheat, beef, pork and some other food products. Will this ruin American farm prices? Be of good cheer. The world prices for soybeans and beef are set by global supply and demand. Soybeans and beef are essentially commodities, not unlike oil. It doesn’t really matter whether China buys American soybeans or Brazilian beans because both those countries are willing sellers. If...