I am not an American, and do not know that country’s politics all that well, but seeing from apart sometimes gives you some interesting sights that people who are closer to the object can’t see, or don’t even realize they see. I think your interpretation of what this book represents and what this whole moment means for the Democratic Party is pretty on the point, and the most interesting part, to me, is that this is a very similar circumstance to what we had with our major “center-left” party here in Brazil , except we elected the center-left candidate (only to see her put the defeated candidate’s agenda in place, and lather be removed while crying that people couldn’t see how bad those who were removing her were — truth be told, they were and are terrible, but it is hard to trust someone who says one thing and acts in a completely different way when it matters). The problem is that the leftist-leaning candidates often think, with reason, that their support base won’t abandon them because the other option is “too dreadful, too horrible”, and then go on to try to bring a center-right agenda, to try to attract support from the center-right (or from the mainstream media, or the party leaders, or corporation. Just everyone “else”). In this reality, obviously, the people is not at fault when and if they abandon the left-leaning (or should I say centrist?) candidate, specially if they look for more solid, more trustworthy options within the left.
I hope the US can deal with the issue better than we did — not that we are over it yet. Now we have to deal with our former president’s right wing vice-president, who is probably one of the worst people to have ever got to office (which in our country is saying a lot).