The answer to your question is simple. In fact, you dance around it in your review! The politics of reform are about navigating the disagreements in the Democratic coalition. Indeed! The point of the book is to present a positive vision of what a Democratic coalition focused around an agenda of demonstrated competency would look like and accomplish. The book is about the persuasive effort.
It doesn't seem plausible that you'd be so unfamiliar with Klein that you didn't know he records one of the most popular policy-driven shows in the country.