 His friendship with prominent politicians and his helping to expose the Glentworth election frauds of 1839 gained him a certain stature in the Democratic Party.He supported James K. Polk for the Presidency in 1844, and was a member of the New York State Assembly (New York Co.) in 1846.In 1846, President Polk offered Stevenson the command of a regiment of volunteers to be raised as part of the American occupation army during the Mexican–American War in California.