Dave Sweeney examines an ear of corn in Alden, Iowa, in 2017. The crop is used for hog feed and the production of ethanol. (Bonnie Jo Mount/Washington Post) FOR MORE THAN a decade, the United States has pursued the foolhardy energy policy known as the Renewable Fuel Standard, or RFS. Thanks to legislation passed by a Democratic Congress and signed into law by a Republican president, George W. Bush, in 2007, the RFS illustrates the sad-but-true principle of…