International Herald Tribune: Backed by the White House, corn-state governors and solid blocks on both sides of Congress’ partisan divide, the politics of biofuels could hardly look sunnier. The economics of the American drive to increase ethanol in the energy supply are more discouraging. American corn-based ethanol is expensive. And while it can help cut oil imports and provide modest reductions in greenhouse gases compared with conventional gasoline, corn ethanol also carries considerable risks. Even now as …