I'm reading the Hagerman book, which isn't as revolutionary as I had heard, but then, older books of analysis can be somewhat underwhelming if you've read the works written since then in reaction. You're getting the points already processed & denigrated or taken into account by those who've followed in the writer's foot-steps.
More striking is the significant number of minor errors of fact, the text often mistaking one river for another - saying so-and-so discussed a 1863 campaign from the Rappahannock to the James, where I'm pretty sure the author meant Rappahannock to the Potomac, or talking about Lee planning a move from Gettysburg to the Rappahannock, where the logic and the actual planning was for a movement behind the Potomac & into the Valley, confusing references to a "Fourth Corps" at a time when there was no such organization with the Army of the Potomac, floating discussions of a "Second Division" without indication of which corps said division belonged to, etc etc. Well, that and all of the nonsense on stilts about Chancellorsville demonstrating the inability of offensive tactical use of artillery & Buford's delaying action before Gettysburg demonstrating the fading of cavalry notions of shock tactics, but those are matters of analysis and not fact.
The reason I bring this up is that Hagerman mentions in passing that Lee was a member of Mahan's Napoleon Club, and this challenged my notions of Lee & my understanding of the events of Lee's life and career. So I went looking online, and the most authoritative online reference I can find is this passage from Freeman's Lee biography. All the other online references are brief notes airily asserting Lee's membership or "sponsorship" in his capacity as West Point commandant. Since those references also erroneously assert that the Napoleon Club was founded several years after McClellan graduated from the Academy, I think I can safely discard them as less than authoritative.
Freeman essentially says that he doesn't know that Lee attended meetings, although he believes that it occurred - the records had been destroyed in a fire, and he spends most of his discussion of the period listing the books Lee took out of the West Point library on military history, instead of on Mahan or the Napoleon Club.
I don't know - the Freeman biography is very old at this point, and perhaps somebody somewhere has done some more work on the subject, but if so, it doesn't show itself online in a quick google. Are there any monographs on the Club, particularly on this alleged sponsorship by Lee as commandant?