Rudy Giuliani never misses an opportunity to remind people about his track record in fighting crime as mayor of New York City from 1994 to 2001. "I began with the city that was the crime capital of America," Giuliani, now a candidate for president, recently told Fox's Chris Wallace. "When I left, it was the safest large city in America. I reduced homicides by 67 percent. I reduced overall crime by 57 percent." While crime did fall dramatically in New York during Giuliani's tenure, a broad range of scientific research has emerged in recent years to show the mayor deserves...