“ While it is appropriate that a single District Judge to whom application is made for an interlocutory injunction restraining the enforcement of a state statute should carefully scrutinize the bill of complaint to ascertain whether a substantial question is presented, to the end that the complainant should not be denied opportunity to be heard in the prescribed manner upon a question that is fairly open to debate, the District Judge clearly has authority to dismiss for the want of jurisdiction when the question lacks the necessary substance and no other ground of jurisdiction appears. ”

“ The question may be plainly unsubstantial, either because it is 'obviously without merit' or because 'its unsoundness so clearly results from the previous decisions of this court as to foreclose the subject and leave no room for the inference that the question sought to be raised can be the subject of controversy.' Levering & Garrigues Co. v. Morrin, supra ”