Good questions, Boss, very good questions. Article VI of the constitution reads, in part:
This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.
Therefore, all precedential rulings are referential to the constitution, if no more so than the question of whether or not they violate a stricture, or fail to coincide with an injuction thereof. So, for example, a judgment given early in our nation's history, when the body of United States precedential ruling was still necessarily small, which might have referred to English common law, could be sustained only to the extent that it was not contradicted by the constitution.
At the time in which Marshall delivered his opinion in
Marbury v. Madison, there was no federal appellate judiciary system other than the Supreme Court, and the only other federal courts were the federal district courts and the courts of common plea in the District of Columbia. Marshall and the other justices of the Supreme Court rode the circuit in each of the Federal Circuits, and sat on the bench to hear the causes brought in appeal. The Congress was at that time in the grip of the Republican Party (only tenuously related to the modern Republican Party, but the direct ancestor of the Democratic Party), which was the only political party on the scene. One was either a Republican, or independent. The Federal Judiciary Act of 1789 had been passed by the First Congress to establish the district courts, but their jurisdiction was restricted. This was a pragmatic move on the part of Congress, a recognition that a nation just lately removed from a bloody war of rebellion against arbitrary power would look with great suspicion on the establishment of a large and powerful court system with the authority to trump their local and state courts. This was why the Justices of the Supremes rode the circuit to hear appeals. (See the text of the Judiciary Act
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But imagine if you will, the power of a government in the grip of the only political party on the scene. Marshall and many of the other Justices feared, and with good reason, that the federal judiciary might be hijacked by the Republicans for precisely the reason you gave--the lack of a body of precedential law which could be used to support federal rulings in conflicts with the states. Mr. Marbury had been appointed a Justice of the Peace in the District of Columbia. His commission, however, was dated in the lame duck period of John Adam's administration, and Adams was by then an extremely unpopular president. He was also virulently hated by the Republicans. James Madison was Jefferson's Secretary of State, and, as the government was constituted then, it was his responsibility to deliver Mr. Marbury's commission to him. He refused to do so, as the Republicans had made it their business to repeal the Judiciary Act of 1800, in which Adams and the dying Federalist Party had attempted to pack the federal bench with new appointments. Since the constitution allows all judges to sits for life,
se bene geserit (so long as well conducted--i.e., personal conduct), the Republicans didn't want to be saddled with judges who owed them nothing and would sit for life. Marbury sued him. The constitution is very clear on such an issue, the Supremes are the court of original jurisdiction in such a matter. The refusal by Madison to deliver the commission was a naked power grab, and it would have gutted the power of the federal bench.
In his opinion, Marshall noted that the constitution makes the Supreme Court the court of original jurisdiction in any action by an individual against the government. He noted that the law clearly required that the Secretary of State was obliged to deliver the commission or a copy thereof from the official record. He determined by logical legal argument that the remedy was a writ of mandamus (a direct legal order of a court) to Madison to deliver the commission. The final question to be considered was whether or not the Court had the authority to issue the writ. Marshall proceeded very carefully to construct the argument that a people would not establish a government by first writing a constitution were that constitution
not to be the supreme law of the land. This was necessary to refute the government's claim that the Court did not have original jurisdiction. If you read Marshall's opinion (rather short, actually, by the standards of the Court), you can see how he constructed this argument. He did this to preserve the authority granted to Federal courts by the constitution, and to cut off the Republican's attempt to put Federal courts under their legislative thumb. Whether or not he foresaw the long-term results for jurisprudence in our nation is unclear; that he wished to preserve the independent authority of the judiciary is clear.
While it is true that no highter judicial authority exists than the Supremes, and that they therefore cannot be reversed--constitutional amendment trumps the court. Therefore, when the hateful racist, Justice Taney, found against the plaintiff in the Dred Scott case, that ruling stood on the basis of what was actually a correct constitutional interpretation, until the XIII amendment prohibited involutary servitude (slavery). When the Supremes threw out the income tax which Lincoln had established to finance the Federal war effort during the Civil War, it was not until XVI amendment was passed that the Feds could again tax personal income. Very often, however, the mechanism is for the Congress to go back to work, and revise the legislation which has been overturned by the Court, so that it will pass constitutional muster. This process keeps everyone on their toes, which i belive was the purpose intended by the "balance of powers" which was written into the constitution. As the
se bene geserit provision is written into the constitution, it is conceivable that if the Court were to overturn legislation for obvious personal prejudice, unsupported and unsupportable by the constitution, one or more of them could be removed under this constitutional provision. So far, such a case has never arisen, and Justices who deliver opinions, whether they've "won" or "lost" their argument in a decision, are always careful to provide a constitutionally referential underpining, or a precedential reference based upon a constitutional interpretation.
The constitution grants to the Supreme Court appellate jurisdiction in specified cases, so that any plaintiff or defendant in a case before a Federal District or Appellate Court can appeal to the Supremes if the judgment goes against them. The Supremes can choose to hear a case, or make a very forceful statement about the value of the "losing" side's argument by refusing to review such a case, at which time the ruling of the last appellate jurisdiction takes on the force of legal precedence (although, of course, the Supremes can later decide to review a similar case, in order to "fine tune" the nature of the legal precedent--the recent ruling on the Texas sodomy case is an example, in that the Supremes had upheld a Georgia sodomy law in 1986, because the law prohibited sodomy by anyone, including married couples, whereas the Texas law specifically outlawed homosexual acts). Your assumption about precedent and the appeal to the Supremes is only partially correct, in that the party which appeals beyond the lower federal court is in essence saying that the interpretation was incorrect, and the Supremes can decide thereafter if they agree. As for the judge in Alabama grandstanding with his ten commandments monument, it is the estimation of legal scholars that the Surpremes will refuse to hear an appeal of the lower court's decision, which would be a heavy judicial slap in the face of the Alabama Chief Justice. It remains to be seen, of course, if this is true. They are not obliged to debate the topic, if they decide his argument has no merit, and refuse to review the decision. If they really want to hurt him, they will hear the case, and refute in detail his every argument--although that is unlikely.
The second paragraph of Section 2, Article III of the constitution defines the jurisdiction of the Supreme Court:
In all Cases affecting Ambassadors, other public Ministers and Consuls, and those in which a State shall be Party, the supreme Court shall have original Jurisdiction. In all the other Cases before mentioned, the supreme Court shall have appellate Jurisdiction, both as to Law and Fact, with such Exceptions, and under such Regulations as the Congress shall make.
So there are a variety of cases in which the Court has original jurisdiction. To the extent that appeals are always based upon a disputed interpretation of statute and/or precedent, yes, the Supremes are usually only consulted on matters touching upon such interpretation.