We all know that soon after the election of Abraham Lincoln, even before his inauguration, the Deep South seceded. But consider: in order for Lincoln to pass any legislation on slavery or any other issue, he would need Congress. In the House, the election of 1860 had been great for the Republicans - they would have entered with a majority even if all Southern seats had been filled. The Senate was a different matter - equal representation for each state gave the South an advantage, and many members from the North were in the middle of their terms, sent there by legislatures when Republicans were not yet so strong. There, the Democrats had a majority, including eight Senators in Free States. Republicans had 28 members. Had the slave states all sent Senators to DC, then those states would have had 30 Senators collectively - not all Democrats, as Maryland had a Unionist Senator - but all likely to uphold slavery if ever it was threatened. So how much of the secession was based in a belief that Northern Democrats in the Senate were untrustworthy partners?
blue -2 R Senators, red - 2 D Senators, green - 1 D/1 R, yellow - 1 D/ 1 R, 30% red - 1 D/ vacant,
gray - seceded by the start of the 37th Congress
The Democratic Convention of 1860 demonstrated the sectional fracture of the party, with the Northern Democrats unwilling to endorse Dred Scot in their platform and supporting a candidate who had opposed the Lecompton Constitution defining Kansas as a slave state. Douglas' popular sovereignty approach didn't work out well in Bloody Kansas so far as the Slave Power was concerned - it was on the verge of joining the Union a free state when Lincoln was elected, and it became so in the same week that Louisiana left. The Southern faction did show their confidence in one Democratic Senator from Oregon enough to make him Breckinridge's Vice Presidential candidate. But some Northern Democrats must have appeared first and foremost Northerners as far as many in the South were concerned.
It may be a stretch to say that there would have been any state seceding with the election of Stephen Douglas. But while pledging he would not undermine Dred Scot, he would have been a change from the more doughface administrations of Pierce and Buchanan, and hardly represented a reliable defender of the peculiar institution under attack. Still nothing could compare to Lincoln and what he represented, and the fear and hostility toward the Republicans may have been more potent than any vote counting. Was there anything in his history to say he would act without the Senate's consent to crush slavery? More influential than anything about Lincoln personally must have been simply that the secessionists read in the very politics of restricting slavery a potential for wholesale Constitutional disregard.
(forgive me if these are obvious statements and questions - the political context of secesssion is just something i've been pondering and want to explore - raising issues that may be tend to be overlooked.)
