James Monroe begins not as a doctrine but as a boy with a musket, a student who left his books at Williamsburg to follow a general across a dark river toward an impossible dawn. Before he was the last of the Virginia dynasty, before editorialists softened the weather of his years into the easy label of an “Era of Good Feelings,” he was nineteen, marching with cold feet and an appetite for risk that had not yet learned to call itself duty. He crossed the Delaware with Washington on Christmas night and took a ball through the shoulder at Trenton in the morning light. That wound did not make him a hero; it made him a witness. He saw how resolve feels when rations are low and shoes fail and the arithmetic of survival becomes a series of small obediences done in hard weather. The soldier became the measure of the statesman he later chose to be: not a  ...