WISCONSIN has been an environmental leader since 1910, when the state’s voters approved a constitutional amendment promoting forest and water conservation. Decades later, pioneering local environmentalists like Aldo Leopold and Senator Gaylord Nelson, who founded Earth Day in 1970, helped forge the nation’s ecological conscience. But now, after the recent passage of a bill that would allow for the construction of what could be the world’s largest open-pit iron ore mine, Wisconsin’s admirable history of environmental stewardship is under attack.