Final answer:
Frederick Douglass campaigned for Abraham Lincoln, the Republican candidate, during the 1860 presidential election.
Step-by-step explanation:
The student asked which presidential candidate Frederick Douglass campaigned on behalf of. During the 1860 presidential election cycle, Douglass, a prominent abolitionist and former slave, supported the Republican Party. While the information provided details various political maneuvers and candidates during the era, it specifically mentions that free blacks such as Frederick Douglass campaigned on behalf of Abraham Lincoln, whom Stephen Douglas labeled as a "Black Republican." Lincoln focused on countering the race issues raised by Douglass, emphasizing his opposition to the dehumanization of black individuals without advocating for full social and political equality.