Yes, many countries allow multi-generational bloodline descendants of their citizens to apply for citizenship, but to start with, NBC status is a status at birth and no mention is made in Vattel for any requirement other than being the child of citizens (father and by extension mother) born on US soil.
To my knowledge SCOTUS has not ruled on this, but at the time the US Constitution was ratified having two US citizen parents one or both of whom were themselves dual citizens or still claimed as citizens by another sovereign (mostly the UK) was widespread. This includes lots of citizens born after the grandfathered date of ratification. But NBC is not defined directly in the Constitution.
It seems clear to me (assuming common usage of NBC came from Vattel) that the founders concern incorporated in the Constitution extended to only whether the legal father was a citizen (and by legal extension the mother).
Knowledge that some fathers were dual citizens was known at the time of ratification, but was not specified as an exclusion for a child to be considered to be an NBC in the writings of the founders including John Jay in his letter to George Washington. Only birth on US soil and the US citizenship of the father and by extension the mother mattered. Any dual citizenship of the father was not discussed but, again, was widely known to be claimed by the UK.
The answer is a simple one. It still takes one generation of naturalized US citizen parents who pass on their US citizenship to their offspring who would be then an NBC to fullfill the Constitional requirement to be president.
In other words, If some foreign state like Italy wants to make multi-generations of Italian descendant citizens they can do that, but the 2nd generation US citizen was what the Founders sought as the threshold and Italy’s citizenship laws do not come into play.
Do you think that if this were to be considered in a modern courtroom, the emphasis on the bloodline of the father would be as important as it was when the Constitution was written? I do not believe it would be so.
As we have all seen, priority is often given to the mother in child custody issues, when it certainly would have been almost unthinkable a) for a woman to instigate a divorce in the 1770’s, and b) get custody of the children if the father didn’t want her to.
I really do not think that “the natural order of things” placing so much importance on the citizenship of the father as opposed to the mother (since we know at this time, the wife would have automatically gone with the husband in terms of naturalization)? Nowadays, we think more in terms of equality of the parents contribution and the mother certainly doesn’t have to share citizenship with the father.
Also, I wonder if any country automatically finds a baby and extends dual citizenship to the child if a parent is from another country than where the baby was born. I know in the instance of my half-Swedish child, she lived in Sweden for four years as an American whose father was Swedish before her dad applied for her to have dual citizenship. Would that qualify for “at birth” do you think, as she could have applied for it (whether we lived or travelled to Sweden or not) from birth?
Obviously, people on the web who aren’t lawyers can’t be sure of their answers being legally correct, but it is an entertaining debate! Thanks!
To add on to my previous post, as long as the duel citizen's children were born in the US, they can pass on a natural born US citizenship to their offspring.