In a rare defiance of the Trump administration, key Senate Republicans joined Democrats Thursday in agreeing to phase down a set of chemicals widely used in air conditioners and refrigeration that is warming the planet. While the Trump administration has balked at embracing a global agreement to reduce hydrofluorocarbons, a dogged push by U.S. firms and environmental groups appears to have overcome the administration's resistance to curbing one of the world's most potent drivers of climate change.