DAVOS, Switzerland – Homeland Security Secretary Michael Chertoff said Thursday the world is facing a critical test as it seeks to keep nuclear weapons out of the hands of terrorists, and that there will be no way “to put that genie back in the bottle” if it fails. Chertoff told a high-level panel on terrorism at the World Economic Forum that the century will only get more dangerous as technology improves, and that global leaders must make some hard decisions now if they want to avert catastrophe. “What we face in the 21st century is the ability of even a...