Trump promised the GOP in Iowa that he would use the EPA to the fullest extent of the law to uphold the ethanol (clean fuels) mandate(and still lost the primary). Unfortunately, that specifies an amount of ethanol to be blended with motor fuels or sold as one outright, which means more alcohol in the fuel if less gasoline is sold. That can exceed 'blend wall' limits of 10%, which will (according to auto manufacturers) cause engine and fuel system damage (older vehicles hardest hit). Any ethanol in fuel is bad for small engines not specifically built to use the fuel (lawnmowers, chainsaws, generators, etc.)