Had Douglas been nominated (and I assume almost certainly elected) in 1856 what sort of VP would he have had. Given that he died in 1861 in OTL his VP is pretty crucial.
I suspect he would have had to have chosen someone from the Ultra Southern wing to be nomineee,.
I am sure that Douglas would not have backed the outragous fraud that was the Lecompton Constitution in Kansas. I think that the plain distortion of 'popular soveriegnty' was a factor in the Republcan sweep in 1860 (along with Dred Scott - which a Douglas Presidency would not have changed.)
Had he been President could Douglas have died EARLIER- the job is stressful, and in those days having access to the best medical care is at best a mixed blessing.
However if Douglas did live to run and win in 1860 I guess an ultra pro slavery President suceeding Douglas would have made the Republican triumph in 1864- and in fact the mid term elections of 1862 rather substantial.