But they didn't.
I didn't. Kentucky v. Dennison is listed in constitutional law texts under chapters dealing with secession. See post #157. I find it quite telling that Texas v. White is barely mentioned.
It doesn't surprise me depending on the slant of the website. But maybe you should read the Dennison decision? Link
Of course they did. Much like Illegal Alien sanctuary cities do today.
There were other cases cases working their way up to the Court. Of particular note was Lemmon v. The People. The New York Court of Appeals held that all slaves -except fugitives- became free the moment they stepped into the state. In dissent it was noted the act would be a valid cause for war. Lemmon was noted as one South Carolinas reasons for secession.
"....slant of the website..."
What website?