I've often wondered about political developments in the US had southern secession been defeated politically by southern Unionists in 1860-1861. In this scenario Lincoln becomes president of a united country with the South in a state of wary watching, ready to try secession if he does some "overt act" against slavery.
In this scenario I believe Lincoln as president would do nothing to openly play into southern fears. However, local state by state events would be a different matter, with local Republican parties gaining strength in the border south area from Missouri in the west to Maryland/Delaware in the east.
I believe Missouri might have become the first state in which a growing Republican party, further nourished by patronage from the administration, would lead the fight for statewide slavery abolition. In the 1860 election, Lincoln and Douglas combined won 45% of the vote, Lincoln winning 10%. Of course its unclear how many Douglas voters would have become future Republican voters, but in 1860, more southern leaning voters could have voted for Bell (who came a close second to Douglas in the state) or Breckinridge.
William Seward wrote in 1858 that with Kansas saved for the free state cause, Missouri would be an upcoming battle in the fight against slavery. According to the book Ballots for Freedom James Rollins, "running on a free labor platform" was almost elected governor. Antislavery candidates had been elected mayors of St Louis and other towns in the 1850's as well.
In this scenario, Republicans would likely gain seats in the Missouri legislature ( I believe they won 12 in the Missouri house in 1860) and field a creditable governor candidate of their own during Lincolns' first administration. A movement toward slavery abolition in Missouri would be about to begin.