Because he was born in Canada, Ted Cruz is ineligible to serve as President of the United States

The point of contention is, exactly, what makes a natural born citizen. In the law, the two essential approaches are jus soli, the citizenship governed by place of birth, and jus sanguinis, the citizenship governed by parentage. You have drawn an unsupported conclusion from an unsupported assertion: yes, one is a natural born citizen from birth; no, not everyone that acquires citizenship via naturalization at birth is a natural born citizen. In fact, Congress exercised its NATURALIZATION power (to make a citizen out of an alien) to extend natural born citizen status to children born abroad to certain categories of American citizens. Thus, because it acted by its Naturalization Power, these fully American citizens are not natural born citizens. The selective partial citation of Blackstone will not do. Blackstone says: "The first and most obvious division of the people is into aliens and natural-born subjects. Natural-born subjects are such as are born within the dominions of the crown of England . . . ." You'll find that here: http://www.gutenberg.org.... Blackstone explained the difference between natives, aliens, or denizens in this important (for our purposes) chapter of his treatise. He states, in the paragraph that you only partially quoted: "When I say, that an alien is one who is born out of the king's dominions, or allegiance, this also must be understood with some restrictions. The common law indeed stood absolutely so; with only a very few exceptions: so that a particular act of parliament became necessary after the restoration[y], for the naturalization of children of his majesty's English subjects, born in foreign countries during the late troubles. And this maxim of the law proceeded upon a general principle, that every man owes natural allegiance where he is born, and cannot owe two such allegiances, or serve two masters, at once. Yet the children of the king's embassadors born abroad were always held to be natural subjects[z]: for as the father, though in a foreign country, owes not even a local allegiance to the prince to whom he is sent; so, with regard to the son also, he was held (by a kind of postliminium) to be born under the king of England's allegiance, represented by his father, the embassador. To encourage also foreign commerce, it was enacted by statute 25 Edw. III. st. 2. tihat all children born abroad, provided both their parents were at the time of the birth in allegiance to the king, and the mother had passed the seas by her husband's consent, might inherit as if born in England: and accordingly it hath been so adjudged in behalf of merchants[a]. But by several more modern statutes[b] these restrictions are still farther taken off: so that all children, born out of the king's ligeance, whose fathers were natural-born subjects, are now natural-born subjects themselves, to all intents and purposes, without any exception; unless their said fathers were attainted, or banished beyond sea, for high treason; or were then in the service of a prince at enmity with Great Britain." So you see Blackstone flatly states that the English common law rule was absolute: "The common law indeed stood absolutely so . . . ." He immediately notes that Parliament extended the boundaries of the common law definition by statute (as I previously explained in Round 2). But in America, we adopted English Common Law and did not adopt English Statute Law (again, for the reasons set out in Round 2, such as the offensive provisions of English Statute Law).