For background, John Fremont was the first Presidential candidate of the Republican Party. He lost the 1856 election to the Democrat James Buchanan. As I’m assuming most people know, the second Republican Presidential candidate, Abraham Lincoln, won in 1860 and several states seceded in response to his election.
But what if Fremont had won in 1856? One possible scenario might have been an early Dred Scott decision. The Supreme Court hearings on Dred Scott were held before the election but the court decided to postpone the delivery of their decision for several months. The controversial decision shifted public opinion in the north from the Democrats (who were seen as puppets of southern slave interests) to the Republicans. If Taney had issued the decision before the election, it might have swung several states to Fremont.
But just assume Fremont won. What would have been the results? Several southern states had threatened to secede if a Republican was elected - would they have followed through? Would it have been all of the same states that seceded in 1860? How would the outgoing Pierce have responded differently than the outgoing Buchanan did? How would Fremont have responded differently from Lincoln? Would it have still come to a war and how would that have been changed by starting four years earlier?