I'm not sure I follow. The case was in US Curcuit court, right? How did Taney rule on a constitutional matter without having the matter before the US Supreme court?
-btw what did Merryman do to get thrown in jail on a suspended writ of habeaus corpus?
Later in this ruling, Taney says:
...a military officer, stationed in Pennsylvania, without giving any information to the district attorney, and without any application to the judicial authorities, assumes to himself the judicial power in the district of Maryland; undertakes to decide what constitutes the crime of treason or rebellion; what evidence (if indeed he required any) is sufficient to support the accusation and justify the commitment; and commits the party, without a hearing, even before himself, to close custody, in a strongly garrisoned fort, to be there held, it would seem, during the pleasure of those who committed him.The constitution provides, as I have before said, that 'no person shall be deprived of life, liberty or property, without due process of law.' It declares that 'the right of the people to be secure in their persons, houses, papers and effects, against unreasonable searches and seizures, shall not be violated; and no warrant shall issue, but upon probable cause, supported by oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.' It provides that the party accused shall be entitled to a speedy trial in a court of justice.
These great and fundamental laws, which congress itself could not suspend, have been disregarded and suspended, like the writ of habeas corpus, by a military order, supported by force of arms. Such is the case now before me, and I can only say that if the authority which the constitution has confided to the judiciary department and judicial officers, may thus, upon any pretext or under any circumstances, be usurped by the military power, at its discretion, the people of the United States are no longer living under a government of laws, but every citizen holds life, liberty and property at the will and pleasure of the army officer in whose military district he may happen to be found.
The federal court system's lower courts make rulings on constitutional issues all the time. Those rulings may be appealed to the Supreme Court, which has the final say in the court system on the matter, but often the supreme court does not take the case or the parties simply abide by the lower court's ruling. To give you some modern examples, the fifth circuit court of appeals has ruled that an affirmative action system is unconstitutional. The rulings in current times apply to that circuit's jurisdiction (unless they are stayed from taking effect), which in the case I just mentioned means the University of Texas cannot use its affirmative action program. That case could be appealed to the supreme court and either affirmed or overturned if the supreme court decided to take it, but until then it is a binding constitutional ruling that requires the University of Texas to not use its previous affirmative action program.
In similar fashion, Taney ruled for the circuit court covering Maryland where Merryman was imprisoned. His decision on constitutionality was therefore binding in the case of Merryman and others under that jurisdiction (Merryman was one of hundreds of Maryland prisoners arrested in suspension of the writ). The Lincoln could have appealed it to the Supreme Court if he believed he could get it overturned. As a side note, a reversal of Taney's decision would have been unlikely as it is a very sound ruling with extensive precedent and historical evidence behind it. I strongly suspect that The Lincoln knew this. He could have still appealed it though as that is the legal procedure. Otherwise he was obliged to follow it. As it happened though, he did neither and simply ignored it. In other times, he could have and likely would have been impeached for such an act.
btw what did Merryman do to get thrown in jail on a suspended writ of habeaus corpus?
He was beleived to be a participant in the secessionist movement for Maryland. No charges were ever specified though due to the writ's suspension. He was released some time later after a continued prison stay without any charges ever filed.