单项选择题

American federalism has been described as a neat mechanical theory. The national government was said to be sovereign in certain areas of governmental concern, such as the regulation of interstate commerce. State governments were said to be sovereign in certain other areas, such as regulation of intrastate commerce and exercise of the police power. One writer has described this as the "layer cake" concept of American federalism. In the top layer are neatly compacted all the powers of the national government; in the bottom layer are found the separate and distinct functions and powers of state governments.
How nice it would be if the American federal system could be so easily and conveniently analyzed. But Professor Martin Grodzins of the University of Chicago has gone on to describe federalism in practice as more like a marble cake, with a mixing of functions, than like a layer cake, with functions separate and distinct. This mixing can be seen best, perhaps, by examining the example of railroad traffic. If it crosses a state line, it constitutes interstate commerce, coming under control of the national government. Rail shipments originating and ending within a single state constitutes intrastate commerce, thus—the theory tells us—falling under regulation of state governments. However, both the interstate and intrastate shipments may have moved over the same rails. In this simple example, one might easily read the urgent necessity for close cooperation between state and national governments. This need has not gone unrecognized by administrators of governmental programs at the state, local and national levels.
Nonetheless, national and state interests often conflict in the political field. Pressures may be brought to bear on state legislators which differ from those felt by members of the national Congress. Disagreement over the proper division of powers between states and the national government often lies beneath a conflict of interests. But no "best" formula has been discovered for drawing a dividing line between state powers and national powers.
The men who wrote the United States Constitution did the best they could in the face of circumstances which confronted them at the time. The state national power dispute has raged persistently ever since. What are "states" rights It is obvious that, throughout United States history, "states" rights have arisen repeatedly as they felt that they were being treated unsympathetically at a given moment by the national government. The source of the cry would seem to depend on whose ox is being gored.
From the author’s point of view, the basic problem in establishing clear guidelines related to interstate commerce would be______.