Insurance executive Tom Knox has made a down payment on a possible candidacy for Philadelphia mayor, transferring $5 million to his new political committee in what amounts to the largest single campaign donation in city history. The Oct. 26 payment from his personal fortune comes as Knox has taken other recent steps toward running for mayor in 2007. His campaign staff is moving into a Center City headquarters this week, a Web site is ready to launch, and aides are planning a series of "listening sessions" with neighborhood leaders. In jump-starting his campaign with cash, Knox joins a small group...