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-- Or we could have millions of citizens who have never lived in the US including grand children and great grand children. Like I said, Congress has the power. Whether they use the power wisely or not is another issue. --

If one applies Vattel, this outcome is precluded.

Vattel: The Law of Nations: Book I

S:215. Children of citizens born in a foreign country.
It is asked whether the children born of citizens in a foreign country are citizens? The laws have decided this question in several countries, and their regulations must be followed.(59) By the law of nature alone, children follow the condition of their fathers, and enter into all their rights (S:212); the place of birth produces no change in this particular, and cannot, of itself, furnish any reason for taking from a child what nature has given him; I say "of itself," for, civil or political laws may, for particular reasons, ordain otherwise. But I suppose that the father has not entirely quitted his country in order to settle elsewhere. If he has fixed his abode in a foreign country, he is become a member of another society, at least as a perpetual inhabitant; and his children will be members of it also.

Vattel notes other potential complications, for example in S:214 ...

Finally, there are states, as, for instance, England, where the single circumstance of being born in the country naturalizes the children of a foreigner.