US Const., Art. I, Sec. 9, cl. 1.
[#17] I suppose it would be within Senator Davis’ interesting views on State sovereignty that each State may regulate or not the slave trade as it sees fit - except that the Constitution reserves that power to Congress.
[#23] US Const., Art. I, Sec. 9, cl. 1.
Section 9.The migration or importation of such persons as any of the states now existing shall think proper to admit, shall not be prohibited by the Congress prior to the year one thousand eight hundred and eight, but a tax or duty may be imposed on such importation, not exceeding ten dollars for each person.
That clause has nothing to do with reserving the power to regulate the slave trade to the Federal government. The whole of Article I, Section 9 places limits on the powers of the Federal government. Clause 1 withholds, from the Federal government, the power to prohibit the importation of slaves until 1808. It neither granted nor reserved any powers.
It does not speak to reserving the regulatory power to the Federal government after 1808. It speaks to importation with regard to the African slave trade. Importation of African slaves was prohibited as of 1/1/1808 and later, in 1820, any American engagement in such trade, anywhere, was made a capital offense. The last hanging was in 1862, with the Captain caught running slaves from Africa to Cuba.
The slave trade discussed in the civil war era did not involve bringing in slaves from Africa.