Once again, Tamar Jacoby and Cesar Conda have demonstrated that they are not serious either about protecting the United States from terrorists or about assimilating immigrants. (See “Immigration Realism.”) Among their criticisms directed at me, they condescendingly dismiss what they take to be my “outmoded ideas about enforcement” — and specifically, the measure permitting local police to check the immigration status of those who violate civil law. I admit it: along with many others — notably John Ashcroft's chief immigration-enforcement official, Kris W. Kobach — I believe that local police should have the authority to check a future Mohammed Atta’s...