[takeit]: I don't know if it was since there is no power delegated to Congress which would indicate it was constitutional.
Lincoln considered it constitutional. I knew that from an 1860 Sam Houston letter I posted on another thread. However, I've just this afternoon discovered on the web two different versions of Lincoln's words proclaiming it constitutional.
The difference concerns the use of the n word. One version might be a PC version cleaned up by Lincoln supporters -- or perhaps the n word was stuck in the other version by hackers.
From Bartleby.com's Great Books On Line (n word version) here is a piece from the October 15th, 1858 Lincoln-Douglas debates (Alton, IL):
I suppose most of us (I know it of myself) believe that the people of the Southern States are entitled to a Congressional Fugitive Slave law,—that is a right fixed in the Constitution. But it cannot be made available to them without Congressional legislation. In the Judge’s language, it is a “barren right” which needs legislation before it can become efficient and valuable to the persons to whom it is guaranteed. And as the right is constitutional, I agree that the legislation shall be granted to it,—and that not that we like the institution of slavery. We profess to have no taste for running and catching ni****s,—at least, I profess no taste for that job at all. Why then do I yield support to a Fugitive Slave law? Because I do not understand that the Constitution, which guarantees that right, can be supported without it.
Essentially the same words but with "ni****s" replaced with "negroes" can be found at this Lincoln Library site: negro version
I suspect the latter is correct since Lincoln uses the word "negroes" throughout the speech except for the spot quoted above.