What I think is interesting as well about the elections of 1852 and 1856 is that a third party (gop) was on the rise, and the whigs essentially went defunct.
The Whigs had already fallen apart by 1856 (the first year that the Republicans ran a candidate for President).
Through 1852, the Whigs finagled the slave issue, intimating that they were for gradual or perhaps compensated emancipation. The big problem, though, is what would have resulted. In the deep South, slaves were the majority of the population. They were uneducated, had no property, and were hardly ready to act as citizens of a democratic republic. So, would they have the right to vote, the right to be witnesses and serve on juries, etc.? Remember that Lincoln, while a Whig, himself finagled the slave issue.
But, this moderate position became untenable. In the South, the Union Party emerged in places to represent Whig interests against the Democrats. In the North, the American Party emerged, combining nativism with Whigishness. In the meanwhile, there was growing dissatisfaction on the slave issue within the Democratic Party. In ‘48, mostly former Democrats running as Free Soil’ers, contested the election.
So, by 1856, the the new American Party, sometimes called the Know Nothings, combined with the what remained of the Whig Party. In the meanwhile, most of the Whigs and the Free Soil’ers combined to form a regional (Northern) party, namely the Republicans. In their first try, the new Republicans were the second party. So, the Republicans were never a third party.
If we were to make a parallel to today, it would be the Libertarians and the independents in the Tea Party movement joining with the majority of the Republicans to form a new major party, call it the Taxpayers Party. Perhaps what remained of the Republicans tried to field candidates. It would be the remnant of the Republican Party, acting as a third party, that would defeat the Taxpayers Party (if they did) and flip the election to their opposite party.
I say let’s take over the Republicans the way the socialists took over the Democrats. No doubt, it will take us a while. But, we are already underway.