Looking a little further into this, it appears that the anti Cruz people are hanging their hat on the fact that only one parent, Cruz's mom, held dual Canadian and U.S. citizenship when Ted Cruz was born. Cruz's dad had only a U.S. green card, which has some stipulations for it to remain valid, when he applied for Canadian citizenship.
The other historical examples, George Romney and John McCain, had two American citizen parents at the time of their birth. Some folks are saying that's the difference here.
Allow me to present a logic flow.
The supreme authority in the United State is the People who, via the Constitution have defined the rules of governance. As such, the Constitution is the highest legal authority and delegates the authority of governance in very specific manner. Some authority is given to the courts, others to the legislature, and others still, to the executive (President).
The Constitution requires that the President be a "Natural born citizen", however, the Constitution does not detail what qualifies as an NBC.
The Constitution does however, vest ALL authority over "the rules of naturalization" with Congress, via Article I, section 8. This authority is exclusive (no authority given to the Courts or to the Executive branch) to Congress AND IS WITHOUT RESTRICTION.
Thus, it is up to Congress to establish the definition of who needs to be naturalized and who does not. Naturalization is an act that only occurs after birth. If a person is born a citizen (citizen at birth) they are naturally born a citizen. One of the first Acts of Congress addresses the fact that children born abroad or over the sea, are citizens at birth and are to be the same as natural born citizens. That act has been repealed and replaced several times.
The current will of Congress regarding who is born a citizen of the United States is expressed in USC title 8 section 1401
https://www.law.cornell.edu/uscode/text/8/1401. Under subsection G:
(g) 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 five years, at least two of which were after attaining the age of fourteen years: Provided, That any periods of honorable service in the Armed Forces of the United States, or periods of employment with the United States Government or with an international organization as that term is defined in section 288 of title 22 by such citizen parent, or any periods during which such citizen parent is physically present abroad as the dependent unmarried son or daughter and a member of the household of a person (A) honorably serving with the Armed Forces of the United States, or (B) employed by the United States Government or an international organization as defined in section 288 of title 22, may be included in order to satisfy the physical-presence requirement of this paragraph. This proviso shall be applicable to persons born on or after December 24, 1952, to the same extent as if it had become effective in its present form on that date; and
...Sen Cruz was born a US citizen and qualified as such via his mother.
