Carter joined the Free Soil Party in 1848, and in 1850 wrote for the Boston "Atlas" a series of articles in reply to Francis Bowen's attack on the Hungarian revolutionists. These articles were republished in a pamphlet as "The Hungarian Controversy" (Boston, 1852). They are said to have caused the rejection of Bowen's nomination as professor of history at Harvard. At the same time Carter edited, with Kossuth's approval, a large volume entitled "Kossuth in New England" (Boston, 1852).