While Turek is correct, I think there's a bit more to it. Lincoln hated slavery but he loved the Union more. This is why he was unwilling to move against slavery where it existed. Without Lincoln there would still be a Republican Party, the North would still tire of the excess political power held by the Slave South and abolition would still be on a slow ascent. But its likely that someone seen as too radical would be nominated by the Republicans in 1860, thus allowing a merged American/Whig Party to survive just long enough to give the Democrats the Presidency in 1860.
If that happens we could see Lemon v. New York end up being decided by the Taney court in a manner that essential opens the entire country to slavery. I still don't think the North would secede but it would create an interesting dilemma. Imagine a nullification crisis in which nearly all the Free States refuse to recognize the ruling and actively move to counter the Fugitive Slave Act. Perhaps the Civil War would start when the President commands the Army to arrest the Governors of several Northern states. That would be very interesting.
Benjamin
