In that you are correct in my opinion. Lincoln would probably not have taken any action to end slavery in the United States. His opinion was that based on the Supreme Court ruling in Scott v. Sanford, he had no constitutional authority to use the Federal Government to interfere with slavery where it was legal. This, however was not the view of some of the Southern States which chose to withdraw from the Union. Their belief was that a Republican controlled House and Senate in unison with a Republican President would, at some point in time, take action to end slavery as it existed in 1860. The only avenue left, in their view, was to withdraw beyond the power of the Federal Government. Hence, secession was the answer to allay their fears.
I can see Lincoln using his "Pen and Telegraph" to enact executive orders that would interfere with it, but I cannot see how the President or the Congress could do anything more than rail about it. No concrete changes could have been enacted.
The Southern reps were not stupid, so I'm finding it hard to grasp how they could have seen an actual threat to their peculiar institution.
I have read others allege and I lean toward's the view that agitation to secede because of slavery was just a means to cover up their real reasons for leaving, which were financial gain.
As the Boston Transcript noted on March 18, 1861:
now the mask has been thrown off and it is apparent that the people of the principal seceding states are now for commercial independence. They dream that the centres of traffic can be changed from Northern to Southern ports . . . by a revenue system verging on free trade. . . . The government would be false to its obligations if this state of things were not provided against.
The difference in sentiment between the North and the South about slavery was a convenient wedge issue to achieve the results they sought in obtaining commercial independence. This is not so remarkable when you noticed Thomas Jefferson said something similar years before.
Six years later the territorial legislature of Missouri asked for admission. The House of Representatives in Washington approved, but attached an amendment requiring that Missouri phase out slavery after statehood. The Senate balked at such a stipulation. . . . Jefferson saw Northern sectionalism conspiring to keep additional Southern states out of the Union. The question of slavery carried with it, according to the former president, “just enough semblance of morality to throw dust into the eyes of the people, and to fanaticize them; while with the knowing ones it is simply a question of power.” (Cisco, Taking A Stand, p. 59)
And
The Missouri question is a mere party trick. The leaders of Federalism, defeated in their schemes of obtaining power by rallying partisans to the principle of monarchism . . . have changed their tack and thrown out another barrel to the whale. They are taking advantage of the virtuous feelings of the people to effect a division of parties by a geographical line. They expect that this will ensure them, on local principles, the majority that they could never obtain on principles of Federalism.(Letter from Thomas Jefferson to William Pinckney, September 20, 1820; cf. Robert Catlett Cave, The Men In Gray, Crawfordville, Georgia: Ruffin Flag Company, 1997, reprint of original edition, p. 134)