He was promoted to First Lieutenant on July 7, 1838, and Captain on March 31, 1850. During this period he served in the Seminole Wars in Florida, the Mexican–American War, and spent 1857–1859 with the Mormon Expedition. In his diaries, he wrote about the Mormon faith with extreme disdain. "Where else than in America could such a flat and puerile invention become enshrined as an established belief. From what trunk except one of the most vigeorous of free institutions could such a fungus of absolutism arise?" In a December 1857 letter he compared Mormonism to a "snake coiled in the desert and concluded that it, like the snake, should be smitten immediately." He was a strong advocate for use of military means to suppress what he viewed as the Mormon threat to American republicanism.