Sen. Lindsey O. Graham (R-S.C.) threatened to abandon his effort to push a climate and energy bill Saturday, saying he will only continue if Democratic leaders promise to relinquish plans to bring up immigration legislation first. Graham's departure, if he follows through on his ultimatum, would likely doom any chance of passing a climate bill this year. He is the sole Republican working with Sens. John Kerry (D-Mass.) and Joseph I. Lieberman (I-Conn.) on a compromise proposal which they had planned to unveil Monday. In a letter to leaders of the effort to enact climate and energy legislation, Graham wrote,...