What is the author's style in Washington, the Indispensable Man by James Thomas Flexner?

The author seems to emulate the style of the people of the time and writes in the passive voice. This style is more difficult to read and takes more time to understand the intent but is in character with the period of the piece. The author is clearly well versed in detail about the people and the reader can almost feel the author holding back so as not to overburden the narrative. One other technique the author uses is to write long paragraphs describing a person or event and then insert a brief summary sentence at the end of that paragraph. This also occurs at the end of each chapter where the author takes the opportunity to briefly summarize for the reader the important facts or activities to take away from that chapter.