William R. Day

“ Acting within the authority conferred by the Constitution it is for Congress to determine what legislation will attain its purposes. The control of Congress over interstate commerce is not to be limited by state laws. Congress, and not the states, is given the authority to regulate interstate commerce. When Congress acts, keeping within the authority committed to it, its laws become by the terms of the Constitution itself the supreme laws of the land. ”

“ The power of Congress, it is true, is to regulate commerce, which is ordinarily accomplished by prescribing rules for its conduct. That regulation may take the character of prohibition, in proper cases, is well established by the decisions of this court. ”

“ When Congress exerts its authority in a matter within its control, state laws must give way in view of the regulation of the subject-matter by the superior power conferred by the Constitution. Seaboard Air Line Rwy. ”