> From the importance of Lincoln's "depressive realism" to the lackluster leadership of exceedingly sane men as Neville Chamberlain

I find these comparisons deeply suspicious. If there indeed were a strong link between leadership ability and mental illness, there cannot be a very big difference between Lincoln and Chamberlain for the reason that both men were surely at the very tails of the relevant distributions. One does not become a British Prime minister by being average. I fully expect the book to be full of cherry-picked data supporting narratives built largely on popular stereotypes about successful and unsuccessful leaders of dubious accuracy.