[plenipotentiary]

The NBC clause was introduced before Naturalised Citizens existed in the US. I ask again, what is the NBC Clause for? Who would it bar?

[Lurking Libertarian]

The NBC clause was introduced before Naturalised Citizens existed in the US.

Nonsense. The states were naturalizing citizens under the Articles of Confederation, which is why the Constitution gave Congress the power to establish a "uniform Rule of Naturalization" (Art. I, sec. 8, cl. 4).