Much like Preston Brooks was not met with condemnation in the South when in 1856 he beat Charles Sumner unconscious on the floor of the Senate while Laurence Keitt held off anyone trying to aid Sumner.
Brooks was sent dozens of canes to replace the one he'd broken over Senator Sumner's head.
Not a valid comparison. Brooks' action, though deplorable, did not threaten anyone except Sumner. Brooks never tried to incite a wave of mass murder across the North. John Brown's raid was an attempt to do exactly that to the South.
Abraham Lincoln said that John Brown’s belief that slavery was wrong did not “excuse violence, bloodshed, and treason.”
Salmon Chase said of Brown’s actions –“How rash – how mad – how criminal.”
William Seward denounced Brown’s Raid as “an act of sedition and treason” and said his execution was “necessary and just”.
Yet Lincoln and Chase and Seward were not the only Republican politicians making statements on the issue. I have personally read some Republican campaign tracts which praised Brown's actions, for example, and others which issued very lukewarm condemnations.
We can argue from here to doomsday about what the Republican leadership really thought about Brown's raid. But the important issue here is not what THEY thought, or even what they said. The important issue is how the South PERCEIVED they thought about it. And a perusal of Southern newspapers of the time will clearly show that it was perceived...whether rightly or wrongly...that the Republicans approved of the raid, and that their policies, as expressed in their platform, would encourage further such incidents.
Remove John Brown and the eloquence he showed after his capture and you reduce the tensions, but there were men in the South who had been pushing for secession long before that.
True enough. And indeed, conventions had been held in the South discussing secession at various times over the years. But public opinion in the South was generally against secession right up to 1860, when suddenly it changed. I would argue that the increased tensions resulting from Brown's raid were the trigger for that change. Nothing you have said disproves that.
Initial fears of a slave uprising quickly faded when the South realized that not a single slave had joined John Brown’s raiders. Which didn’t mean people weren’t afraid of their slaves – there was the Texas Fire Scare of 1860 and Laurence Keitt’s brother was actually murdered by his slaves.
Well, it may be true that people didn't fear an IMMEDIATE uprising after John Brown went to the gallows. But fear of an uprising, aided by extremists from the North, did play a very central role in Southern thinking during the 1860 campaign. Again, a perusal of Southern newspapers and political speeches of the time clearly shows that.
Actually, the split in the Democratic Party was over the party platform. The South walked out of the Democratic Convention before they began to vote on a candidate.
The Northern Democrats Platform supported slavery. It said it would abide by the Supreme Court’s decision (the same one that had rendered the Dred Scott decision) about slavery in the territories. It called for the annexation of Cuba, long favored by Southern leaders as a way to add more pro-slavery territory. It condemned attempts to evade the Fugitive Slave Law as hostile, subversive, and revolutionary.
That wasn’t enough for the Southern Democrats. Their Platform repudiated Popular Sovereignty and said that the inhabitants of Territories had no right to restrict slavery in the Territories. It also said that Congress had no right to restrict slavery in the Territories.
All of which makes one ask, why, all of a sudden, are they adopting such an extreme position? Again, I would argue that the evidence points to fallout from John Brown's raid and it's effect on the Southern psyche at the time. And again, nothing you have said disproves that.
Looking at the electoral vote, Lincoln still would have won handily if the Democratic Party had not split.
That's true, as far as it goes. But it ignores several important factors. The electoral vote split was 169 for Lincoln versus 134 combined for the other candidates...a margin of only 35 votes. Several of the States which went for Lincoln did so by relatively narrow margins, and might have gone the other way if the South was perceived as being less extreme by the North. In Ohio, Indiana, and Illinois, where he won with 52.3%, 51.1%, and 50.7% of the popular vote respectively, there were more than enough electoral votes to swing the election. For that matter, Lincoln won New York with only 53.7% of the popular vote, and New York had 35 electors at the time...enough to have changed the result all by itself had it gone Democratic in a hypothetical Douglas v. Lincoln race.
The insistence by the South on the extreme pro-slavery platform at the Democratic Convention, which you mentioned previously, and the fact that they chose to split the Democratic Party over the issue, was a major factor in that perception on the part of Northern voters. Remove John Brown, and the South probably doesn't insist on the extreme platform in the first place...which means the South is perceived as being less extreme by Northern voters, some of whom vote for Douglas instead of Lincoln. Under those conditions, given a united Democratic Party and a straight 2 way race, Douglas most probably wins.