602
CONSTITUTION OF THE U. STATES.
[BOOK III.
to the courts of the United States, must not the state court proceed to hear, and determine it? Can a mere plea in defence be, of itself, a bar to further proceedings, so as to prohibit an inquiry into its truth, or legal propriety, when no other tribunal exists, to whom judicial cognizance of such cases is confided? Suppose an indictment for a crime in a state court, and the defendant should allege in his defence, that the crime was created by an ex post facto act of the state, must not the state court, in the exercise of a jurisdiction, which has already rightfully attached, have a right to pronounce on the validity, and sufficiency of the defence? It would be extremely difficult, upon any legal principles, to give a negative answer to these inquiries. Innumerable instances of the same sort might be stated, in illustration of the position; and unless the state courts could sustain jurisdiction in such cases, this clause of the sixth article would be without meaning or effect; and public mischiefs, of a most enormous magnitude, would inevitably ensue.
It must, therefore, be conceded, that the constitution, not only contemplated, but meant to provide for cases within the scope of the judicial power of the United States, which might yet depend before state tribunals. It was foreseen, that, in the exercise of their ordinary jurisdiction, state courts would, incidentally, take cognizance of cases arising under the constitution, the laws, and treaties of the United States. Yet to all these cases the judicial power, by the very terms of the constitution, is to extend. It cannot extend by original jurisdiction, if that has already rightfully and exclusively attached in the state courts, which (as has been already shown)
