A deluge of political scandals hasn’t sunk EPA Administrator Scott Pruitt. But a wonky debate over the nation’s biofuel policy just might. Republican Senator Chuck Grassley bluntly warned last month he would call for Pruitt’s resignation if the Environmental Protection Agency continued exempting small oil refineries from a mandate to use renewable fuels such as ethanol made from corn, a staple crop in his home state of Iowa. When Pruitt moved to do what Grassley wanted — with a plan that would force larger refineries to make up for the waivers by using more biofuel — he sparked an intense, angry uproar among oil executives and allied lawmakers who telephoned top Trump administration officials to complain. Their not-so-subtle message: Pruitt’s job was on the line. […]