In 1854, Knapp ran as an anti-slavery Free Soiler and was elected overwhelmingly to Congress as a member of the American Party (the only major party with an anti-slavery plank) to the Thirty-fourth Congress.
In 1854, Knapp ran as an anti-slavery candidate and was elected to the United States House of Representatives. He was identified with the American Party (the only major party with an anti-slavery plank) while serving in the Thirty-fourth Congress.