Which presidential aspirants are taking the best advantage of podcasting's potential?  A review of the candidates' offerings on iTunes shows John McCain and Rudy Giuliani as no-shows.  Hillary's well-done video chats don't show up in iTunes, but there is an old podcast in the directory which doesn't do much to help her, and she should take it down ASAP.  At the head of the presidential podcasting class are Tom Vilsack, John Edwards, and Barack Obama.  Mitt Romney has an effective enthusiast's site up, MyManMitt.com featuring the MittCast, hosted by Justin Hart.  This episode of the Audio Pod Chronicles, recorded in Denver, contains excerpts from the podcasts and thoughts about what works and what doesn't in this powerful new medium.