As a result of Metcalf's opposition to slavery, in 1855 he was nominated for Governor by the Know Nothing movement, one of the few parties with an anti-slavery plank in its platform. This effort was promoted by Free Soil Democrats including John P. Hale, who hoped to create a movement that would send New Hampshire anti-slavery activists to the United States Senate and help build the nascent Republican Party. (It worked—Hale was elected to the Senate in 1855, eventually moving to the Republican Party because of his views on slavery. James Bell, an abolitionist identified with the Opposition Party also won a Senate seat in 1855, and later became a Republican.)