What from the prologue to Theodore Rex should I focus on to teach it to a class?
The prologue to Theodore Rex by Edmund Morris focuses on a re-telling of the assassination of President McKinley in 1901 and the ascendancy of Teddy Roosevelt (TR) to the Presidency. While the prologue is told in a narrative format, it also emphasizes several themes of TR's life and his future presidency that you could focus on while teaching.
When President McKinley was shot, TR was in the Adirondacks, and Morris uses this passage to emphasize how TR developed his physical courage. He writes, "Although his physical courage was now legendary, it was not a natural endowment" (page 6). This passage allows readers to focus on TR's upbringing and his concerted effort to advance himself, first by lifting weights when he was a child and then by moving up the ladder of political life. This passage is an insight into TR's past, including his stint as "Rough Rider" in the Spanish-American War.
As TR boards the train to Buffalo, where McKinley was shot, Morris concentrates on several of the problems TR will face. His train is like his own presidency, which is now under steam. He first thinks about how to handle anarchism and the problems posed by people like Czolgosz, the anarchist who shot McKinley. He then thinks about America's destiny in the new century.
After taking the oath of office and reassuring McKinley's cabinet that they will retain their positions for now, TR takes a train to Washington. The point of this part of the narrative is in part the energy of the U.S. at the turn of the century, and this is what you might focus on in this part. As the train gathers speed, Morris writes about the productivity of the nation and the global reach of its manufactured goods.
The other themes that Morris touches on in this part of the narrative are the foreign policy situation TR will face (including his partnership with Edward VII in Great Britain against the German Kaiser and the Russian Tsar and TR's desire to build a canal in Panama). As TR's train heads to Washington, TR also thinks about combating the powers of the great monopolies in American business and, as he passes through Pennsylvania, TR thinks about how to help miners and American labor. Finally, he focuses on how to help reform the situation of America's working class to bring about reform. His thoughts as he travels to Washington cover several themes of TR's presidency, including foreign policy, the Industrial Revolution, his eventual trust-busting activities, and his reforms to help labor and the poor. These are points you could focus on while teaching.