OOC: Seconded.
IC: It might be delayed, as per Johnny Martin's excellent 'Confederacy' trilogy(2 published in 1960, and the other in 1962), which had VP and later, SecState Lincoln, of all people, winning in 1860 on top of Buchanan.
The official Steve Jackson fan series from 1977 later extrapolated, all the way out into 1976 in fact, about the ATL history of the U.S.(and the world to a lesser extent) after the war. Surprisingly enough, there are quite a few similarities to OTL, such as Teddy Roosevelt winning two terms in office(and a cousin of his wins four terms, and leads us right through this universe's World War 2....or most of it, anyway), the creation of a Soviet Union in Russia(though ours was much less screwed up. Only Steve Jackson could come up with a guy like Joseph Stalin......), and even drops a tribute to OTL baseball player John E. Carter(though his counterpart's from Georgia and named Jimmy: John Carter was from Missouri originally). And they both make it work so well.
Anyway, John C. Fremont may have been from S.C. originally, but he was hated even more than even Abe Lincoln, let alone James Buchanan, would have been, simply because he was viewed as, in the words of Alexander Stephens, "A goddamn traitor to kith and kin", for his increasingly radical anti-slavery attitudes above all else.