I highly recommend "Don't Think of an Elephant!" to anyone interested in progressive politics. The book is very well written, easy to read, concise, and important.
The basic premise is that, over the last few decades, republicans have gotten good at framing issues in terms that implicitly support their worldview. Democrats have used the republican framings and language even when trying to argue for progressive policies, but using the republican framing has the neurological effect of reinforcing the republican framing.