It was interesting that the slave power seemed to think that peace and harmony between the races would be assured if as Chief Justice Taney asserted, their was no law regarding the Negro that the White man needed to honor. Of course that was myth, since free Negros of North Carolina had the vote until 1835, and Negroes were permitted to sue and defend them selves from assault in various states.
Slavery was not withering away, but rather was becoming more onerous, and more profitable since the invention of the Cotton Gin by northerner Eli Whitney.
I can’t seem to locate it, but in one of his speeches Lincoln talks about how slavery had been made more harsh in recent years. To be fair this was largely because southerners felt their institution was under attack and natural human tendency is to crack down in defense.
That it was becoming more profitable is easily seen by prices, which reached their all-time high in 1860. Even slaveowners don’t bid up the price of a capital asset unless they think its future prospects for income are also increasing.