Is he saying most people would support slavery? What an idiot. Even before the Civil War, why do you think Lincoln was elected? He ran as an abolitionist.
He’s saying people would try and bring back slavery today.
He did no such thing.
He recognized that under the Constitution the federal government had no power to interfere with slavery in a state, and said so publicly many times.
Most abolitionists didn't care what the Constitution said, in fact some of them denounced it and publicly burned it.
Lincoln campaigned in favor of prohibiting the spread of slavery into new areas, not of abolishing it in the states where it existed.