From the very beginning of his service in Congress , Hamlin was prominent as an opponent of the extension of slavery . He was a conspicuous supporter of the Wilmot Proviso and spoke against the Compromise Measures of 1850 . In 1854 , Hamlin strongly opposed the passage of the Kansas – Nebraska Act , which repealed the Missouri Compromise . After the Democratic Party endorsed that repeal at the 1856 Democratic National Convention , on June 12 , 1856 , he withdrew from the Democratic Party and joined the newly organized Republican Party , causing a national sensation
1856 Democratic National Convention
1856 Democratic National Convention
Hannibal Hamlin