The reason defining natural born citizenship was never a problem before the now is because of something called "derivative citizenship." Before the mid 1920s all women held the citizenship of either their father if single or their husband if they were married. This means that if a Irish man married an American woman, the woman would also become Irish. However, if an American man married an Irish woman, then the Irish woman became an American citizen. Consequently, if a couple was married with an American Father it was pretty much impossible to have anything but a Natural born citizen. (In the case of illegitimate children, the children received the father's citizenship unless the father was unknown in which case they inherited the mothers citizenship.) This system was rejected by the progressives as too "patriarchal", but that is the reality of it. Most of the Western world used to pass citizenship through the father.
Only now that the government allows a husband and wife to hold different citizenships independent of each other do we have confusion.
Yes, I knew that citizenship was very much tied to the Father in the past, but if one posts everything on knows or would like to know on a subject, the post would be waaaay toooo long. LOL.