The first election in which the D was left-wing and the R was right-wing

[Rockefeller GOP]

This will upset those living in liberal fantasy land, but on fiscal issues it was 1856.  Period.  The GOP has always been a pro-business party, and I honestly find it 100% revisionist and biased to call defending slavery (as Southern Democrats did) socially conservative and trying to tie that to conservatism of today, while also completely ignoring that some of the fiercest abolitionists were from devoutly conservative Christian denominations like the Quakers.  The Second Great Awakening and the explosion of moralism that followed (something Democrats still mock Republicans for today) did a heck of a lot more to advance anti-slavery sentiment than this revisionist notion that the charge was led by these intellectual progressives of the day.  When you throw in that the other main group that opposed slavery was the Northern business community, which argued it interfered with the ideal of a free market with free labor, it doesn't sound liberal or left wing at all to me ... I guess if you repeat something loud enough and often enough, it becomes accepted as truth.