New York City Mayor Michael Bloomberg gave the inaugural Presidential Lecture at Dartmouth yesterday. It was a very engaging hour, spent roughly half in lecture mode and half in Q&A. I think mayors are fascinating people to put in front of students. Most public policy issues have a local dimension, and in many cases -- health, education, the environment, for example -- local actors will play very important roles. And mayors are the people we elect to get things done. According to Bloomberg, what's the most important public policy issue facing the nation? Immigration.