What Is This Change You're Promising?

In discussing an argument against selecting Hillary (the I'll-keep-him-at-arms-length-generally George Will had said "She would be a potent unifier of John McCain’s party"), John Cole writes:

What Obama offers us is the chance, no matter how slight to change the conversation from “Who do I vote against?” to “What is this change you’re promising, and why should I vote for you?”