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.
In the third place, the rejection of the Wilmot Proviso and the acceptance (as regards New Mexico and Utah) of "Squatter Sovereignty" meant the adoption of a new principle in dealing with slavery in the territories, which, although it did not apply to the same territory, was antagonistic to the Missouri Compromise of 1820.
