It's interesting that even though Lincoln didn't win a majority of votes in the country, he did win a majority in the states he carried, except for California, Oregon, and that messy situation in New Jersey. If the Democrats and other anti-Republican forces had gotten behind a single candidate and Lincoln had lost those three states but carried the rest, he would still have won the election, and there could have been a situation where a candidate with under 40% of the popular vote won the electoral college and the election.
That would really have been an explosive situation, and you might well have seen fighting in the major cities of the North as well as in the South. A candidate who gets less than 40% in a two-way election is a lot less viable or acceptable than one who wins about 40% in a four-way race.
Somehow, though, I don't see that happening. The results were what they were because people sensed that the divided Democrats (and the old Whigs of the John Bell faction) weren't going to win. A united Democrat or anti-Republican ticket would have looked better and could have carried some of the Lincoln states where the margin was narrow.
I'd suppose that secessionist forces pushed for the party split precisely because it was more likely to bring about a Republican's election and the secession of the Deep South states. Even if we assume they were acting wholly in good faith, it's hard to see which Democrat could have satisfied both the Deep South and the Northern swing states.
The cotton states hated Douglas. An actual Southerner wouldn't have played well in the North, and an Easterner might still have lost to Lincoln in the West (today's Middle West). A win in New York and New Jersey, though, would have thrown the election to the Democrats. But as we've seen in recent elections, the candidates who can win elections don't always exist when parties want them.
Can you imagine that 1860 election today?
There's have to be an issue as divisive as slavery was 150 years ago. A lively three-party race is just barely possible. A four-way race much less so. This may be an upside of our ideological politics. One side or the other is going to win. A third party just might arise, but there's not room for more than that (unless it's something like a regional candidate who senses that the country is already breaking up and wants the most for his own section).
“If the Democrats and other anti-Republican forces had gotten behind a single candidate and Lincoln had lost those three states but carried the rest, he would still have won the election, and there could have been a situation where a candidate with under 40% of the popular vote won the electoral college and the election.”
And that was my point. The south saw that this was the case, CA and OR notwithstanding.