The fact is that the combine vote totals in each of Northern states for all candidates other than Lincoln did not add up to 50% of that states total vote. So it would seem to indicate that even if there had been only one Democrat candidate against Lincoln the Democrats would have lost anyway. WHY?
What did Lincoln say or do in his campaigning that gave him such an overwhelming vote turnout? Was that it? Did the Democrats just not turn out to vote because of the contriverse in the Democrat party in the northern states?
I don't know how to compare the Democrat vote totals in 1860's. Were they lower that expected? Were they normal? We know that the south went solidly for Breckenridge. But to have won the election the Democrats would have had to have won at least some of the Northern states.
While it is true that the combined popular votes of the Democrat candidate was 2,823,975 to Lincolns 1,865,563, it was the electorial college votes were Lincoln beat the Democrats 180 to 123. So it was the electorial college votes of 17 northern and western states that gave Lincoln his victory. 17 out of 33 State then in the Union. So even had the south voted solidly for a single Democrat that candidate would have still needed to win one or two of those northern states to have beat Lincoln.
It would seem that the balance of power within the Congress and presidential electorial politics shifted with the admission of California and Oregan to the Union.