James Buchanan runs and wins the election of 1856 without promising not to run for a second term. He then runs in 1860 as (likely) the sole democrat challenging republican nominee (likely) Abraham Lincoln.
Does he win? If so, what does this mean for the early 1860s and the slavery issue?
(I'm aware that the reason he wanted out after one is because he foresaw the civil war, but in this alt. hist. he doesn't because of a change in thought process or being convinced otherwise)
Why on earth do you think that he would be the sole Democrat? The Douglasites won't accept Breckinridge but they will accept Buchanan whom they hated far more?! (At least Breckinridge, despite his disagreements with Douglas on the Freeport Doctrine and the Lecompton Constitution, supported him for re-election against Lincoln in 1858. By contrast, Buchanan was determined to purge the Democratic party of Douglasites, even if it meant electing "Black Republicans.")
The 1858 elections had shown what a pariah Buchanan was in the North--even in his own state of Pennsylvania. Douglas did win in Illinois, but even with the legislative apportionment favoring the Democrats, he only won because he had repudiated Buchanan's position on slavery in the territories. (Which was basically that not only could neither Congress nor territorial legislatures prohibit slavery in the territories, but had a positive duty to protect slavery there.)
And even the pro-Southern wing of the Democrats could see that Buchanan could not be re-elected--not only because of the unpopularity of his position on slavery in the North, not only because the Panic of 1857 had revived economic issues like the tariff in the North (especially in Pennsylvania), but because of the corruption in his administration, which would be a drag on his ticket in all sections. Indeed, the Republicans made corruption one of their major issues--they didn't call Lincoln *Honest* Old Abe for nothing...
In the unlikely event that the pro-southern wing of the Democrats nominates Buchanan, there will be a four-way race as in OTL--Buchanan, Douglas, Lincoln, and Bell. Buchanan has no more chance of winning such a race than Breckinridge did--indeed, even less.