Again, the States themselves had a clear right to waive the constitutional privilege intended for their benefit, and to prohibit by their own laws this trade at any time they thought proper previous to 1808.  Several of them exercised this right before that period, and among them some containing the greatest number of slaves.  This gave to Congress the immediate power to act in regard to all such States, because they themselves had removed the constitutional barrier.  Congress accordingly passed an act on 28th February, 1803, “to prevent the importation of certain persons into certain States where by the laws thereof their admission is prohibited.”  In this manner the importation of African slaves into the United States was to a great extent prohibited some years in advance of 1808.

As the year 1808 approached Congress determined not to suffer this trade to exist even for a single day after they had the power to abolish it.  On the 2d of March, 1807, they passed an act, to take effect “from and after the 1st day of January, 1808,” prohibiting the importation of African slaves into the United States.  This was followed by subsequent acts of a similar character, to which I need not specially refer.  Such were the principles and such the practice of our ancestors more than fifty years ago in regard to the African slave trade.  It did not occur to the revered patriots who had been delegates to the Convention, and afterwards became members of Congress, that in passing these laws they had violated the Constitution which they had framed with so much care and deliberation.  They supposed that to prohibit Congress in express terms from exercising a specified power before an appointed day necessarily involved the right to exercise this power after that day had arrived.

If this were not the case, the framers of the Constitution had expended much labor in vain.  Had they imagined that Congress would possess no power to prohibit the trade either before or after 1808, they would not have taken so much care to protect the States against the exercise of this power before that period.  Nay, more, they would not have attached such vast importance to this provision as to have excluded it from the possibility of future repeal or amendment, to which other portions of the Constitution were exposed.  It would, then, have been wholly unnecessary to ingraft on the fifth article of the Constitution, prescribing the mode of its own future amendment, the proviso “that no amendment which may be made prior to the year 1808 shall in any manner affect” the provision in the Constitution securing to the States the right to admit the importation of African slaves previous to that period.  According to the adverse construction, the clause itself, on which so much care and discussion had been employed by the members of the Convention, was an absolute nullity from the beginning, and all that has since been done under it a mere usurpation.