The word "natural" appears in only two places in the original Constitution of the United States, both of which refer to citizenship. In Article II, the Constitution provides that to be eligible to serve as President a person must be a "natural born citizen." And in Article I, the Constitution vests Congress with the power to establish a uniform rule of "naturalization." Accordingly, the words of the original Constitution set forth two ways that a person can become a citizen. A person may be born a citizen, or a person may be naturalized as a citizen. No other options are described in the text of the Constitution.
The first words of the Fourteenth Amendment, which was drafted shortly after the Civil War, added the "Citizenship Clause" to the Constitution. It states:
All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside.Once again the words of the Constitution identify two ways and only two ways that a person can become a citizen -- by birth or by naturalization. The Fourteenth Amendment, it is true, affirmatively provides that a person who is born in the United States automatically becomes a citizen of the United States. But it does not prohibit persons born abroad to an American parent from being considered citizens. Nor does it state that only persons who are born in the United States are "natural born" citizens.
Ted Cruz was not naturalized. Instead he became a citizen at the moment of his birth. It is true that he was born in Canada, but since the time of the founding federal statutes have granted citizenship to persons born abroad to an American parent, so long as the parent resided in the United States for a certain prescribed period of time. Ted Cruz's mother was a citizen of the United States and she did in fact reside in the United States for the statutorily-prescribed period of time, so under federal statutes Ted Cruz became a citizen at the moment of his birth.
Cruz is not a citizen by virtue of the Citizenship Clause of the Fourteenth Amendment of the Constitution. He is however a citizen by virtue of federal statutes that confer citizenship on persons born abroad to a parent who is an American citizen. Accordingly, Ted Cruz became a citizen at birth -- a "natural born citizen" -- and is therefore eligible under the Constitution to seek the office of the Presidency.