Linking to this succinct but powerful essay by Paul Clement and my Georgetown colleague Neal Katyal, Jonathan usefully summarizes the legal argument for why Ted Cruz, who was born in Canada to an American mother, is a “natural born citizen” under Article II, section 1 of the Constitution, which provides:

No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution,shall be eligible to the Office of President; neither shall any Person be eligible to that Office who shall not have attained to the Age of thirty five Years, and been fourteen Years a Resident within the United States. (emphasis added)

As he concludes in his post: “Under U.S. law, the fact that Cruz was born to a U.S. citizen mother makes him a citizen from birth. In other words, he is a ‘natural born citizen’ (as opposed to a naturalized citizen) and is constitutionally eligible.” To the evidence elicited by Clement and Katyal, I wish only to add that this conclusion is also theoretically justified by a proper conception of popular sovereignty.

The term “natural born citizen” had no existence or independent original meaning prior to the moment it was included in the Constitution the United States was founded. It was adapted by the framers [of the Constitution] from the well-known British concept of the “natural born subject” of the sovereign monarch. England had numerous and changing legal rules governing exactly who was and who was not a “natural born subject,” which can be used to muddy the waters. But one consistently applied rule is particularly germane: The offspring of the King were natural born subjects of the King regardless of where they were born, whether on English territory or not.

In the United States, We the People are the sovereign. In my forthcoming book, Our Republican Constitution: Securing the Liberty and Sovereignty of We the People,” I explain how the Declaration of Independence implies an individualist conception of We the People and that it is “to secure” the individual rights of the people that governments are established. This individualist conception of popular sovereignty was articulated by Chief Justice John Jay and Justice James Wilson in the Supreme Court’s first great constitutional case of Chishom v. Georgia in 1793.

As Justice Wilson put it, laws “derived from the pure source of equality and justice must be founded on the CONSENT of those whose obedience they require. The sovereign, when traced to this source, must be found in the man,” meaning the individual person. He then referred to the states as “an aggregate of free men, a collection of original sovereigns.” Chief Justice Jay affirmed the “great and glorious principle, that the people are the sovereign of this country,” and he then immediately referred to Americans as “fellow citizens and joint sovereigns.” Notice the plural use of “sovereigns” by both.

Like the evidence cited by Clement and Katyal, an individualist conception of We the People and “popular sovereignty” supports the same conclusion: just as the offspring of the sovereign monarch are “natural born subjects” of the realm regardless of where they are born, so too are offspring of the sovereign individual citizen “natural born citizens” of the United States, though they may be born outside its borders. Who is the sovereign, not territory, is what matters. In the United States, it is We the People, each and every one.

UPDATE #2: I see now that David Upham reached the same conclusion, albeit tentatively, for the same reason back in March. In Ted Cruz: A Probable Natural-Born Citizen of the American Republic he concludes:

All authorities seemingly concurred that the offspring of the King, regardless of place of birth, were plainly the King’s “natural-born subjects.”  No statute was ever needed to make such persons “subjects.”  Indeed, as Blackstone added, even the King’s ambassadors, because of their representative capacity, likewise carried abroad, by extension, the movable bodily sovereignty of the King: “the children of the king’s embassadors born abroad were always held to be natural subjects.” Unlike children born abroad to ordinary subjects, these children required no parliamentary naturalization at all—they were always deemed “natural-born.”
In our republic, however, the citizens became the sovereign.  As Chief Justice John Jay wrote in Chisholm v. Georgia,  “at the Revolution, the sovereignty devolved on the people; and they are truly the sovereigns of the country…; the citizens of America are equal as fellow citizens, and as joint tenants in the sovereignty.”  If so, then the citizens of the American Republic arguably carry with their bodies abroad this sovereignty just as the King and His ambassadors had.  Consequently, since 1776, any child born to a member of the sovereign citizenry of the United States is as much a “natural-born citizen” of our Republic as a child born to the sovereign King was the natural-born subject of the British monarchy.
Ted Cruz, then, is probably a natural-born citizen of the United States, not because he was a citizen “from birth.”  Rather, he is a natural-born citizen because at his birth, he was the offspring of one of the Queens or Kings that compose the American Sovereign.

Great minds and all that… Although I have never before published on this subject (no pun intended), Larry Solum did credit me in his 2015 article Originalism and the Natural Born Citizen Clause with having privately made this point to him.

UPDATE: My post erroneously stated that the phrase “natural born citizen” was devised by the framers of the Constitution, when in fact it had been previously used in state constitutions after the founding of the United States.  See, for example, here. Although this does not affect the substance of my point about how the change from “subject” to “citizen” results from a shift from monarchical to popular sovereignty at the founding, I do regret the error (now corrected), which was based on my misrecollection of an article on the subject.