Oddly enough, the Breckenridge-Lane ticket was on the ballot in even more northern states. Their best showing outside the slave states was 37.5% in Pennsylvania.
A lot of Northerners did not want to go to war over slavery; neither did a lot of southerners. Both sides were plagued with recruiting problems throughout the war due to these feelings. The cost of the war in treasure alone was more than ten or twelve times the value of the slaves at the market peak.
What generally happened with the Democrats is that the party machine in the state decided if they favored Douglas or Breckenridge and the Democrats in the state went along with that. The Democrats were divided on the West Coast, so both Douglas and Breckenridge were competitive in California and Oregon. In Pennsylvania, New Jersey, New York and Rhode Island ran "fusion" slates of electors who would vote for Douglas or Breckenridge depending on how things looked when the electors voted. New Jersey voted for a mix of Republican and Democrat electors so Lincoln and Douglas both got electoral votes from the state. Lincoln carried the other three states, but there was a split between the Fusion ticket and Douglas loyalists in Pennsylvania, so it looks like a lot of people favored Breckenridge when they were voting for the Democrat party line, rather than a small group of rebellious Douglas loyalists.
Not so fast...
1860 total US assets were put around $16 billion, of which $3-4 billion were slaves.
Farms totaled around $7 billion, with railroads & manufacturing combined $2.3 billion.
The Civil War cost the Union $6 billion, plus another $3.5 billion in pensions for veterans over the next 50 years.
Confederates spent around $2 billion, plus Southern states an unknown amount for Confederate veterans.
Destruction of non-slave property in the South was significant, maybe $1 billion.
Yes, the $value of lost lives is incalculable, but actuarily speaking, based on $600 average annual income, perhaps another $10 billion.
So, if we assume the higher value for slaves and ignore actuarial values of lives lost, then the Civil War cost about double the value of US slaves in 1860.
Yes, if we take the lower value of slaves ($3+ billion) and include actuarial values as costs, then the war cost about seven times the 1860 value of US slaves.
On the other hand, similar to WWII, the Civil War hugely increased US manufacturing infrastructure setting the stage for the late 19th century US economic & industrial growth miracle.