What they thought at the time:
http://www.librarycompany.org/republ...56campaign.htm
And the campaign issues of the 1856 election:
http://dig.lib.niu.edu/message/campa...tory-1856.html
The Republicans selected Fremont because of his opposition to the Fugitive Slave Laws, and according to the second article many prominent southerners vowed to secede if Fremont were elected. Did they actually fight each other, or beat each up in the Senate over State Sovereignty issues? Not that I've heard of.