You apparently need a refresher on Marbury vs. Madison, where the Court defined its own jurisdiction and took a power not explicitly granted to it by the Constitution.
The decision in Marbury vs. Madison in part said this:
"If an act of the legislature, repugnant to the constitution, is void, does it, notwithstanding its invalidity, bind the courts, and oblige them to give it effect? Or, in other words, though it be not law, does it constitute a rule as operative as if it was a law? This would be to overthrow in fact what was established in theory; and would seem, at first view, an absurdity too gross to be insisted on. It shall, however, receive a more attentive consideration.
It is emphatically the province and duty of the judicial department to say what the law is. Those who apply the rule to particular cases, must of necessity expound and interpret that rule. If two laws conflict with each other, the courts must decide on the operation of each.
So if a law be in opposition to the constitution; if both the law and the constitution apply to a particular case, so that the court must either decide that case conformably to the law, disregarding the constitution; or conformably to the constitution, disregarding the law; the court must determine which of these conflicting rules governs the case. This is of the very essence of judicial duty.
If then the courts are to regard the constitution; and the constitution is superior to any ordinary act of the legislature; the constitution, and not such ordinary act, must govern the case to which they both apply.
Those then who controvert the principle that the constitution is to be considered, in court, as a paramount law, are reduced to the necessity of maintaining that courts must close their eyes on the constitution, and see only the law.
This doctrine would subvert the very foundation of all written constitutions. It would declare that an act, which, according to the principles and theory of our government, is entirely void; is yet, in practice, completely obligatory. It would declare, that if the legislature shall do what is expressly forbidden, such act, notwithstanding the express prohibition, is in reality effectual. It would be giving to the legislature a practical and real omnipotence, with the same breath which professes to restrict their powers within narrow limits. It is prescribing limits, and declaring that those limits may be passed at pleasure.
That it thus reduces to nothing what we have deemed the greatest improvement on political institutions -- a written constitution -- would of itself be sufficient, in America, where written constitutions have been viewed with so much reverence, for rejecting the construction. But the peculiar expressions of the constitution of the United States furnish additional arguments in favor of its rejection.
The judicial power of the United States is extended to all cases arising under the constitution. Could it be the intention of those who gave this power, to say that, in using it, the constitution should not be looked into? That a case arising under the constitution should be decided without examining the instrument under which it arises? This is too extravagant to be maintained.
In some cases then, the constitution must be looked into by the judges. And if they can open it at all, what part of it are they forbidden to read, or to obey? There are many other parts of the constitution which serve to illustrate this subject. It is declared that "no tax or duty shall be laid on articles exported from any state." Suppose a duty on the export of cotton, of tobacco, or of flour; and a suit instituted to recover it. Ought judgment to be rendered in such a case? ought the judges to close their eyes on the constitution, and only see the law. The constitution declares that "no bill of attainder or ex post facto law shall be passed."
If, however, such a bill should be passed and a person should be prosecuted under it; must the court condemn to death those victims whom the constitution endeavors to preserve?
Why otherwise does it direct the judges to take an oath to support it? This oath certainly applies, in an especial manner, to their conduct in their official character. How immoral to impose it on them, if they were to be used as the instruments, and the knowing instruments, for violating what they swear to support!
The oath of office, too, imposed by the legislature, is completely demonstrative of the legislative opinion on the subject. It is in these words, "I do solemnly swear that I will administer justice without respect to persons, and do equal right to the poor and to the rich; and that I will faithfully and impartially discharge all the duties incumbent on me as according to the best of my abilities and understanding, agreeably to the constitution, and laws of the United States."
Why does a judge swear to discharge his duties agreeably to the constitution of the United States, if that constitution forms no rule for his government? if it is closed upon him, and cannot be inspected by him?
If such be the real state of things, this is worse than solemn mockery. To prescribe, or to take this oath, becomes equally a crime.
Thus, the particular phraseology of the constitution of the United States confirms and strengthens the principle, supposed to be essential to all written constitutions, that a law repugnant to the constitution is void; and that courts, as well as other departments, are bound by that instrument."
By this decision, the Court established for itself a jurisdiction that the Constitution did not explicitly give it. Nowhere does the Constitution give the Court the specific right to declare acts of Congress unconstitutional. This decision had the effect of the Court defining its own jurisdiction.
Moreover, in this decision, the Court made itself the sole arbiter of the Constitution and the final authority on what the Constitution means. This pretty much defeats your proposition that the Court cannot define for itself its role under the Constitution. The case of Marbury vs. Madison proves your argument fallacious.
Furthermore, you haven't demonstrated that in Texas vs. White, there was any new definition of a role for the Court by its decision. All you have done is asserted your proposition to be true but that is hardly authoritative. You have also not stated why this decision does not have the force of law. Certainly the disputants in the case as well as everyone else took it as law, so it sure LOOKS like law to me.
So once again, your argument fails.
Your main assertion is that secession is a policy matter. To a certain extent, that is true. However, the Court is the sole arbiter of the Constitution as Marbury vs. Madison shows. The Court stated that the Constitution does not empower an individual state to secede, that this power has been taken away from states. This makes the issue of secession also a legal one in addition to the policy question you are focusing on.
Since the decision of the Court in Texas vs. White was predicated on the powers of the state as being bound by the Constitution of the United States, the Court was well within its purview to make the determination it came to. The Court certainly has the power to determine if actions by states are constitutional and has had this power since Marbury vs. Madison. Therefore, the Court was charting no new role for itself in Texas vs. White.
Which means only that secession was illegal despite the sputterings of neo Confederates.
