H. Draper Hunt, "Hamlin, Hannibal," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-00459.html.
In 1843 Hamlin was elected to Congress, serving two terms in the House. Hamlin fought at John Quincy Adams's side to rescind the "gag rule," which barred abolitionist petitions from consideration by the House. He opposed Texas annexation on antislavery grounds and saw the Mexican War as a southern plot to expand the "peculiar institution." Hamlin helped formulate the Wilmot Proviso, which proposed to ban slavery from any territory acquired from Mexico.