But although much has been said, in the discussion on former occasions, about this supposed concurrent power in the States, I find great difficulty in understanding what is meant by it.  It is generally qualified by saying, that it is a power by which the States could pass laws on subjects of commercial regulation, which would be valid until Congress should pass other laws controlling them, or inconsistent with them, and that then the State laws must yield.  What sort of concurrent powers are these, which cannot exist together?  Indeed, the very reading of the clause in the Constitution must put to flight this notion of a general concurrent power.  The Constitution was formed for all the States; and Congress was to have power to regulate commerce.  Now, what is the import of this, but that Congress is to give the rule, to establish the system, to exercise the control over the subject?  And can more than one power, in cases of this sort, give the rule, establish the system, or exercise the control?  As it is not contended that the power of Congress is to be exercised by a supervision of State legislation, and as it is clear that Congress is to give the general rule, I contend that this power of giving the general rule is transferred, by the Constitution, from the States to Congress, to be exercised as that body may see fit; and consequently, that all those high exercises of power, which might be considered as giving the rule, or establishing the system, in regard to great commercial interests, are necessarily left with Congress alone.  Of this character I consider monopolies of trade or navigation; embargoes; the system of navigation laws; the countervailing laws, as against foreign states; and other important enactments respecting our connection with such states.  It appears to me a most reasonable construction to say, that in these respects the power of Congress is exclusive, from the nature of the power.  If it be not so, where is the limit, or who shall fix a boundary for the exercise of the power of the States?  Can a State grant a monopoly of trade?  Can New York shut her ports to all but her own citizens?  Can she refuse admission to ships of particular nations?  The argument on the other side is, and must be, that she might do all these things, until Congress should revoke her enactments.  And this is called concurrent legislation!  What confusion such notions lead to is obvious enough.  A power in the States to do any thing, and every thing, in regard to commerce, till Congress shall undo it, would suppose a state of things at least as bad as that which existed before the present Constitution.  It is the true wisdom of these governments to keep their action as distinct as possible.  The general government should not seek to operate where the States can operate with more advantage to the community; nor should the States encroach on ground which the public good, as well as the Constitution, refers to the exclusive control of Congress.