The several points of the Dred Scott decision, in connection with Senator Douglas's "care not" policy, constitute the piece of machinery, in its present state of advancement. This was the third point gained. The working points of that machinery are:
Firstly, That no negro slave imported as such from Africa, and descendant of such slave, can ever be a citizen of any State, in the sense of that term as used in the Constitution of the United States. This point is made in order to deprive the negro, in every possible event, of the benefit of the provision of the United States Constitution which declares that "The citizens of each State shall be entitled to all privileges and immunities of citizens in the several States."
Secondly, That, "subject to the Constitution of the United States," neither Congress nor a Territorial Legislature can exclude slavery from any United States Territory. This point is made in order that individual men fill up the Territories with slaves, without danger of losing them as property, and thus to enhance the chances of permanency to the institution through all the future.
Thirdly, That whether the holding a negro in actual slavery in a free State makes him free, as against the holder, the United States courts will not decide, but will leave to be decided by the courts of any slave state the negro may be forced into by the master. This point is made, not to be pressed immediately; but, if acquiesced in for a while, and apparently indorsed by the people at an election, then to sustain the logical conclusion that what Dred Scott's master might lawfully do with Dred Scott, in the free State of Illinois, every other master may lawfully do with any other one, or one thousand slaves, in Illinois, or in any other free State.
Auxiliary to all this, and working hand in hand with it, the Nebraska doctrine, or what is left of it, is to educate and mould public opinion, at least Northern public opinion, not to care whether slavery is voted down or voted up. This shows exactly where we now are; and partially, also, whither we are tending...
Why was the amendment, expressly declaring the right of the people, voted down? Plainly enough now, -- the speaking out then would have damaged the "perfectly free" argument upon which the election was to be carried. Why the outgoing President's felicitation on the indorsement? Why the delay of a reargument? Why the incoming President's advance exhortation in favor of the decision? These things look like the cautious patting and petting of a spirited horse preparatory to mounting him, when it is dreaded that he may give the rider a fall. And why the hasty after-indorsement of the decision by the President and others?
We cannot absolutely know that all these exact adaptations are the result of preconcert. But when we see a lot of framed timbers, different portions of which we know have been gotten out at different times and places and by different workmen, -- Stephen, Franklin, Roger, and James, for instance, -- and when we see these timbers joined together, and see they exactly make the frame of a house or a mill, all the tenons and mortises exactly fitting, and all the lengths and proportions of the different pieces exactly adapted to their respective places, and not a piece too many or too few, -- not omitting even scaffolding, -- or, if a single piece be lacking, we see the place in the frame exactly fitted and prepared yet to bring such piece in, -- in such a case, we find it impossible not to believe that Stephen and Franklin and Roger and James all understood one another from the beginning, and all worked upon a common plan or draft drawn up before the first blow was struck...
Source: Roy P. Basler, ed., Collected Works of Abraham Lincoln, vol. 2 (1953), 461-68.