And the nature of the clause tells us that there was a definition at the time of the writing. The founders would have defined it in the clause if it did not exist and they were creating some new definition. It did exist in the Law of Nations, so no new definition was required in the Constitution. Two US citizen parents at birth produces a NBC. Very simple.
This strangest thing for me is that, forgetting the birth certificate, everyone on the planet knew when he started running for office that his father, in addition to his stepfather, were NOT American citizens. And no one said a word in the media. Not on our side or theirs. Not rush, hannity, Anyone.
For purposes of discussion, let's assume you are right. A Supreme Court decision would still be required to determine precisely how the passage of the 14th Amendment will have affected the issue.
A definition was also found in English common law, but a very different one. The Court will have to decide which of these two meanings the Founders were using.
It really is not self-evident, and such shades of meaning are exactly what the Court is supposed to determine.