Now, both parties have had their fair share of politicians that have occupied both the left and right of the spectrum. As we know, today the Democrats occupy the left (sort of) and the Republicans the right however this wasn't always the case.
What would have to happen for a left-wing republican party and a right-wing democrats to rise. What would both these parties look like, what would their main issues be? Who would be their major bases (i.e. stronghold states, the people they would appeal to etc).