A one-sentence provision buried in the Senate’s recently passed energy bill, inserted without debate at the urging of the nuclear power industry, could make builders of new nuclear plants eligible for tens of billions of dollars in government loan guarantees.

U.S. coal mining companies, which for years have been branded the bad guys of global warming, are fighting back. They are questioning not only the science but also the motives of some of the big-name corporations who have made well-publicized commitments to cleaning up their act.