And then Douglas was of no use to them. The rebs would have dropped Democratic stalwart Douglas for any high tariff, big government Whig had that man gone for slavery everywhere. I suspect that if Douglas had somehow been elected there would have still been a secession eventually. Once the slave interest got their heart set on the territories, a conflict was inevitable whether the rebs were in or out of the Union.
If there was any economic cause to the Civil War, it would have been that the South was wading in such a deep pool of cash that they believed they really could take on a section that had three times their white population.
The 1850s had spoiled them, emboldened them and finally infuriated them as the belated reaction from the nation threatened their dreams of a slavery utopia just when it seemed in their grasp.
Few people realize that the Confederacy's ultimate goal - as articulated by the fire-eaters and proclaimed by David Atchison - was to seize as much federal territory as they could, annex California, annex Baja California or all of Mexico, annex Nicaragua and Honduras and also Spain's Caribbean possessions - especially Cuba and Puerto Rico.
All of this with the eventual goal of reopening the slave trade.
The only reasons why the Confederate Constitution excluded the reopening of the slave trade were the knowledge that Virginia would not secede unless it were excluded (VA had a slave surplus and profited from sales of excess slaves to the deep South - a reopened slave trade would have caused prices to plummet) and the UK would never intervene.