[Aurelius]

"Texas v. White, 1869."

Eight years after South Carolina seceded, in other words, hence irrelevant so far as their secession was concerned. Or were the South Carolinians supposed to prophetically anticipate the Court's decision of 8 years later and recognize their intended action as illegal thereby.

[Non-Sequitur]

Eight years later? Yes. Irrelevant? No. What it shows is that while the people of South Carolina thought that act of unilateral secession was legal they were wrong. Their actions were illegal.