@Thomas,
Prior to the adoption of the 14th amendment, there really wasn't any "American citizenship." Instead, if you were a citizen of a state, then you were perforce a citizen of the United States. The only people who were "American citizens" were naturalized citizens. That actually was one of the issues in the
Dred Scott case -- whether a slave, who couldn't be a state citizen, could nevertheless be a citizen of the US. Chief Justice Taney answered with a pretty definitive "no."
The 14th amendment, of course, changed all of that. Now, a person is a citizen of the US if they're born in the US. Furthermore, there's no rational distinction between the "natural born Citizen" in Art. II of the constitution and the "persons born ... in the United States" in Sec. 1 of the 14th amendment, and no one has, to my knowledge, attempted to make a distinction until now. Both clauses are referring to the same kind of "citizen."