Stanley Karnow had it right when he said many years ago that a reporter’s toolkit consists of two main things: background knowledge and skepticism. He might have added that a good supply of shoe leather helps as well. I was reminded of Karnow’s maxim by the death on March 14 of Alan Krueger, 58, of Princeton University. I was sad to think I hadn’t seen Krueger or spoken to him since 2011, when he became chairman of President Obama’s Council of Economic Advisers, succeeding Austan Goolsbee. At first I thought the lapse must have been a function of my having…