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Since its establishment five years ago, the Department of Homeland Security has played a pivotal role in mobilizing the efforts of the United States government to prevent and deter terrorists and other dangerous people from attacking the country. These efforts have yielded positive results: By any fair measure, the United States is safer and more secure today. Yet it would be a mistake to conclude that the threat posed by terrorism has entirely disappeared or has ceased to be of critical concern. In the words of the July 2007 National Intelligence Estimate, "[W]e face a persistent and evolving terrorist threat over the next three years." In al Qaeda and like-minded organizations, the United States and its allies confront a...
