US citizenship can pass through either parent. Being born in the US is sufficient in and of itself regardless of the citizenship of your parents. That's the "what and why" of anchor babies. The laws regarding citizenship at birth have changed over time. The statute at the time of 0's birth, the one that would apply, was this:
1952 The Immigration and Nationality Act of June 27, 1952, 66 Stat. 163, 235, 8 U.S. Code Section 1401 (b). (Section 301 of the Act).
"Section 301. (a) The following shall be nationals and citizens of the United States at birth:
"(1) a person born in the United States, and subject to the jurisdiction thereof;
"(7) a person born outside the geographical limits of the United States and its outlying possessions of parents one of whom is an alien, and the other a citizen of the United States, who prior to the birth of such person, was physically present in the United States or its outlying possessions for a period or periods totaling not less than ten years, at least five of which were after attaining the age of fourteen years."
The specific facts that determine 0's citizenship are where and when was he born? He claims to have been born in HI on August 4, 1961. The date is not in dispute, but the location is. At the time of 0's birth his mother was 18 years 8 months 6 days old. That means that at the time of 0's birth, discounting all the travel time outside of the US, the maximum time she could have resided in the US after the age of 14 was 4 years 8 months 6 days. That she was a citizen at the time is not disputed. That the father was an alien from Kenya, and a British subject, is not disputed. The dispute is as to the location of 0's birth. If he was born in Kenya then he was not a citizen because his citizen parent (mother) did not meet the residency requirements.
Now, as to whether he is natural born or not, the Constitution only distinguishes two types of citizen: naturalized or natural born. If you are born a citizen you are natural born, if you, at some point after you were born, had to go through a process to become a citizen, you are naturalized. There is no third "born a citizen but not natural born" category. There is no Constitutional basis for it. There is no basis in law. It doesn't exist.
"So you can see that the founders did not allow dual citizenship, for even a naturalized citizen."
The founders did not allow naturalized citizens to have dual citizenship - they wanted new citizens to commit fully or not at all. It has no bearing on natural born citizens, else dual citizenship for any US citizens would be impossible and that is certainly not the case. The 1952 statute makes no reference to dual citizenship at all. The US law doesn't care what other nations might consider you a citizen, for the most part, but expects you to renounce any foreign allegiance upon reaching adulthood (some other countries do not, Canada, for instance). We have no evidence that 0 did or did not renounce his British citizenship, but there is no formal or official process that I am aware of so we can't dispute it. Further, there is no requirement that you remain a citizen, only that you be born a citizen, so if 0 is hiding a change of citizenship he isn't violating the Constitution (except in spirit) in that regard.
Really, the only disputed factor is where he was born. HI=natural born US citizen, Kenya=British subject at birth.
George Romney’s parents, although both were citizens of the U.S., did not qualify George to become legally the President of the U.S. because he was born in Mexico and therefore a citizen of the U.S. but Not a natural born citizen. According to the Constitution one has to be a natural born citizen. The reverse could also happen that two people sneak over the border and have their child here. The child is a US citizen, but again he is not natural born, because his parents are citizens in Mexico. The child could also claim dual citizenship and have loyalty to Mexico and the USA
You cannot be a natural born citizen, if you were not born on US soil. Children born on overseas military bases are not natural born citizens. Current State Department policy reads: “Despite widespread popular belief, U.S. military installations abroad and U.S. deplomatic or consular facilites are not part of the United States within the meaning of the 14th Amendment. A child born on the premises of such a facility is not subject to the jurisdiction of the United States and does not acquire U.S. citizenship by reason of birth.”
The US Constitution Article ll section 1. It says “No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constituion, shall be eligible to the Office of President; niether shall any Person be eligible to that Office who shall not have attained to the Age of thirty five Years, and been fouteen Years a Resident within the United States.” Many people get this all wrong too. It says “No Person except a natural born Citizen” - “or a Citizen of the United States, at the time of the Adoption of this Constitution,”. Many people misread this line and think that any citizen can be President, but what it was saying is either a natural born Citizen OR any citizen who was alive at the time the Constitution was adopted. Unless you know of any candidates that are 256 years old, the President must be a Natural Born Citizen.
If you look at the United States Naturalization Law of March 26, 1790, it states “the children of citizens of the United States that may be born beyond Sea, or out of the limits of the United States, shall be considered as natural born Citizens”. So we can learn from this that you have to be the child of US citizens, to be a natural born citizen.
Now that law was repealed and replaced by the The Naturalization Act of 1795 which now stated that “the children of citizens of the United States born out of the limits and jurisdiction of the United States, shall be considered as “citizen of the United States.” “This act, signed into law by George Washington himself, dropped the “natural born” phrase. So from this we can see the only way you can be a natural born citizen, is to be born to US citizens on US soil.