I'm just going to quote several bits (but really -- read the whole thing), in each case from Hans, and then I'll have a few comments:
The key insight of the book is to look at presidential nominations not from the point of the view of the people trying to get the nomination, but from the point of view of the party that’s trying to bestow it...And so we should tell the story from the point of view of the players in the party who have an opinion about who the nominee should be and can do something about it.
[The party's] goals are to find a nominee who can win, but who is also someone they can trust. Whether they can trust them because they’re in the right place ideologically is part of it, but it’s richer than that. It’s someone who they think will advance party goals over their own personal goals.
I should add, we spend a lot of time in the book talking about who has the most endorsements. But the argument isn’t that whoever has the most endorsements wins. It’s that whoever the party is supporting wins, and endorsements are one way of getting at that.It's really outstanding, and lots of credit to Greg Marx and CJR.
Regular readers will know that I agree with Hans pretty much down-the-line, and he does an excellent job of making the case very clear and easy to follow.
If there's one difference I'd have, it's in emphasis. Hans and his co-authors generally stress co-ordination problems and how parties go about solving those in the presidential nomination process. I think they get there because their empirical puzzle was to show how parties learned to overcome those problems after reform in 1968-1972, and fair enough; that's a great question, and I think they answer it well. I'd probably put a bit more emphasis, however, on internal party differences, and the nomination process as a means of settling those fights. In other words, it's not always about "the party" coming to agreement about which candidate to support; it can also be, in part, a fight over what and who "the party" is going to be.
Sometimes, those fights spill out to the primaries and caucuses. Sometimes, probably more often, they are settled internally. In my view, primaries and caucuses are used more (as they were prior to reform) to gather information about electability, at least for those party actors who care about that (which is most, but not necessarily all, of them).
Anyway, go read the whole thing.