This had to be a spoof.

See:

Hannibal Hamlin, who served as a Representative, Governor, and Senator from Maine before the 1860 election, had a dark complexion, and was widely rumored in the South to have African-American ancestry. The fire-eater R. Barnwell Rhett said in a July 9, 1860 speech that “Hamlin is what we call a Mulatto…they design to place over the South a man who has Negro blood in his veins.” Some modern writers repeat the rumor as a source of African-American pride, but it doesn’t seem to have any basis in fact.
http://gathkinsons.net/sesqui/?p=1327