The facts of the case are well-known and not in dispute. Dred Scott was a slave owned by an army surgeon named John Emerson. During his time with the army, Emerson was posted to Rock Island, Illinois (a free state) and Fort Snelling, Minnesota (a free territory via the Missouri Compromise), and in both cases Scott accompanied his master. After Emerson died, Scott was advised by friends to sue in court to obtain his freedom, claiming that the sojourns in Illinois and Minnesota had freed him. (One thing about American jurisprudence has not changed; Scott first filed his suit in 1846 and the Supreme Court did not hear the case until 10 years later.)
Scott lost in most of the state courts but was able to continue his appeals because Scott's owner had now moved to New York and so the case could be moved to Federal Court. Thus the matter eventually reached the Supreme Court, which rendered its decision on March 6th, 1857. The decision is universally regarded as one of the worst pieces of legal reasoning ever to be issued by the Supreme Court.
The Court voted (in a confusingly fractured decision), 6-3, to deny Scott's petition. The majority opinion (itself a mis-nomer, since there were eight opinions issued) was written by Chief Justice Taney, and has been controversial ever since.
Taney's argument contained two main points:
The very nature of the decision struck at the core belief of the Republican Party, for it made it plain that proscribing the expansion of slavery was just as difficult as abolishing it. In addition, the decision was viewed by many as a watershed in the relationship between slavery and the Federal government. Prior to Dred Scott, many would have said, the United States Constitution tolerated slavery but did not protect it. After the decision, there was no denying that the Constitution -- at least in Taney's view -- did indeed protect it. Moreover, the very logic of the decision was fraught with pitfalls and contrary precedents.
Taney's contention that a black man was not a citizen and had no standing to sue was contradicted by at least one Federal precedent and a host of colonial ones. His contention that the Constitution did not allow Congress power to proscribe slavery on the territories flew in the face of much evidence from the writing of the national document, including the votes of several of the Framers in support of the Missouri Compromise. (The most ironic of these would be the statement of George Mason in the Constitutional Convention, that "the general government should have the power to prevent the increase of slavery." George Mason's son, James Mason, was, a senator from Virginia and author of the Fugitive Slave Act of 1850.)
What bothered the free states the most, though, was that there was nothing in Taney's logic to prevent it from being used to allow slavery in any of the states. Essentially, Taney asserted that the Fifth Amendment's protection of property was in this case superior to the Constitution's provision that Congress make all needful rules and regulations for the territories. Nor was this an empty fear. A New York case was working its way through the appeals process in the latter half of the decade which might well have been the case that Southerners were looking for. If Dred Scott's two year sojourn in Illinois did not make him a free man, how long could a slaveowner claim the right to stay on free soil and keep his slaves? (Curiously, in 1851 the South Carolina Supreme Court had recognized that taking a slave to a free state released him from bondage.)
In addition to the furor over the nature and logic of the decision, there was an equal furor over the surrounding atmosphere. The decision was announced two days after President Buchanan's inauguration, and there was much suspicion of collusion between the President, Taney, and Southern interests. Senator Seward's charges in this regard were so blunt that Taney later declared he would have refused to administer the oath of office to Seward if the New Yorker had won the Presidency in 1860.
While many of the specific charges of the day were not supportable, it turns out that there was some less than ethical behavior going on in the background. Alexander Stephens is suspected of putting pressure on Justice James Wayne of Georgia ("I have been urging all the influence I could bring to bear on the Sup. Ct. to get them no longer to postpone the case on the Mo. Restriction;" from a letter to his brother Linton, quoted in Battle Cry of Freedom.) And there is substantial evidence that Buchanan exhorted his fellow Pennsylvanian, Justice Robert Grier, to join the five Southern justices in voted the Missouri Compromise down, and that he was in communication with some of the other justices during the period of time when the decision was being developed. Grier's conversion to Taney's side was significant, for it changed the decision from 5-4 to 6-3, and gave it a non-sectional coloration.
Modern legal scholars have argued to this day over the merits of Taney's decision. One issue concerns whether or not the decision was an example of obiter dictum, meaning a statement in passing on matters not before the Court, and therefore not a matter of law. The thrust of this argument is that once Taney decided that Scott had no standing to sue, there was no point or reason to declare the Missouri Compromise unconstitutional Nevins seems to agree that the decision was an obiter dictum, while McPherson says (page 175) otherwise.
Politically, the Dred Scott decision was a lot like Douglas's Kansas-Nebraska Act -- something done to settle the slavery question, which in fact inflammed it. Buchanan and Taney appear to have wanted to attack the Republican Party by placing their fundamental creed -- limitation of slavery -- beyond the reach of Congress, while the Southern element wanted to re-establish the potential for the expansion of slavery. The price that was paid was in fact a stronger Republican Party, which was able to use the Dred Scott decision to buttress their claims of a Slave Power that was running national affairs for sectional gain. When Abraham Lincoln was invited east in 1860 for a speaking tour -- an event that essentially established him as a serious dark-horse candidate for the Republican nomination -- his premiere speech at Cooper Union was a tour de force on the historical and legal precedents which stood opposed to Taney's decision.