President Barack Obama, bypassing a politically divided Congress, is expected to use his executive authority under the Clean Air Act to impose the new rules. Obama's unannounced plan already is fueling talk of legal challenges, debates over whether meeting emissions goals in each state will kill jobs and raise costs to consumers, and questions of whether the world's other major coal-burning nations—particularly China—will follow the United States' lead in trying to curb carbon emissions. (See related story: "Ahead of Proposed U.S. Power Plant Rules, the Spin Scramble Begins.")

It also could ring in a new era of carbon regulation that will be felt especially in coal-burning states such as those in America's rust belt. The president's plan is likely