In the spring of 1871, Ulysses S. Grant wrote to an old friend that as president he was "the most persecuted individual on the Western Continent." Grant had not sought the office, and halfway through his first term he chafed under its many burdens. Grant's cherished project to annex Santo Domingo, begun early in his administration, entered a crucial period. Grant agreed to a tactical compromise: Rather than vote the controversial treaty down,...