The commerce clause has become the authority for exercising the enormous powers of the national government as is illustrated, possibly, by the exercise of power under no other clause. This means that the United States in exercising this delegated power exercises so vast a power that it seems to be sovereignty itself. Vast as this power is—and practically it is incommensurable—it is a delegated, not an original power of the national government. The scope, purpose, and nature of this national power to regulate commerce are indicated by the Supreme Court in its construction of the commerce clause. Here as in the exercise of the taxing power the test is jurisdiction. The essential question is, What is the jurisdiction of the United States, what that of the respective States over commerce? 53. Commerce is intercourse,[134] and comprehends traffic, navigation, telegraphic intercommunication, and consequently, communication by telephone, wireless, or signals.[135] The Constitution empowers Congress to regulate commerce “among the several States,” an expression which excludes “the completely interior traffic of a State.” This completely internal commerce is reserved for the State itself. To whatsoever extent the foreign or interstate commerce of the United States penetrates a State, it is subject to regulation by the United States; it is carried on within national jurisdiction. The power of Congress to regulate commerce within this jurisdiction is complete in itself and knows no limitations other than these prescribed in the Constitution. Thus this power to regulate commerce, though limited to commerce with foreign nations and among the States, and with the Indian tribes, is plenary as to these objects, and Congress in exercising this power is commonly spoken of as “sovereign.”[136] It follows, that as the Constitution is the supreme law of the land, and the Supreme Court has power to say what the law is—State laws to regulate commerce, in conflict with national laws, are unconstitutional. The essential issue, in such conflict, is one of jurisdiction. And here, the real question is whether the regulation of commerce by a State is essential to its existence as a State, or regulation by the United States is essential to its existence as the United States. Such regulation by a State is known as the exercise of the police power.[137]