While he was in Congress he voted repeatedly for the principle of the Wilmot Proviso.
Later when the conservatives accepted the annexation of Texas and the radicals supported the Wilmot Proviso the split became irrevocable.
He voted for the bill to exclude anti-slavery literature from the mails, approved of the annexation of Texas, the war with Mexico, and the Compromise of 1850, and disapproved of the Wilmot Proviso.
He loyally supported Polk's administration during the Mexican War, opposed the Wilmot Proviso, and advocated the Compromise Measures of 1850 and the Kansas-Nebraska Bill of 1854.
Wilmot, The Life and Times of Sir Richard Southey (1904); Sir J.