What is the author's style in American Sphinx by Joseph Ellis?

The structure of American Sphinx resembles a series of academic essays relating to Jefferson at various points in his life. Ellis tries to present a snapshot of Jefferson at different crucial periods. Unfortunately, there is seldom enough detail about Jefferson's life and personality to bring these snapshots into clear focus. Instead, the information is presented around a few main themes within each section. The themes present Ellis's own points of view without much corroborating evidence. There is never an explanation of how Ellis arrived at his conclusions or any allusion to possible different perspectives. The result is that the reader knows much less about the facts of Jefferson's life than about Ellis' own opinions.