As just about everyone knows by now, Sen. Ted Cruz was born in Canada, to a Cuban-born father and a mother who was a U.S. citizen. Cruz held Canadian citizenship for nearly all of his life, relinquishing it only in 2014 when he was planning to run for the presidency.

Is he eligible to hold the office he seeks?

This is a question of constitutional law, not of politics. Respected analysts have shown that the question is not simple to answer. The Constitution states that the president must be "natural born," but doesn't define that term. The Supreme Court has never ruled on the issue; if it did, it would find a murky history.

Under a narrow interpretation, natural born means that you were born within the territorial boundaries of the U.S. Under a broader interpretation, it means that you were a citizen at birth and did not have to undergo a naturalization process.

The text of the Constitution doesn't exclude either interpretation. The word "natural" might be taken to require birth in the U.S.; in the 18th century, natural was often opposed to "provided by statute" — suggesting that to serve as president, you must have been born in the country, rather than being recognized as a citizen through an act of Congress. But a natural-born citizen might be someone who just is a citizen at the moment of birth, as Cruz plainly was (through the citizenship of his mother).

William Blackstone was an important influence on the founding generation; his views receive respectful attention in U.S. courts. In 1765, he explained that natural-born subjects "are such as are born within the dominions of the crown of England." He noted that "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."

Blackstone added that the English parliament had made exceptions, as for those born abroad to two English parents and, later, for those whose fathers were natural born. Cruz does not meet Blackstone's test (which tracks 18th-century British law). In any case, the exceptions might suggest only that a national legislature can treat certain people, for purposes of citizenship, as if they were "natural born" — not that they are, in fact, natural born.

In terms of the American founding itself, there is no clear support for either the narrow or the broad interpretation. Those who favor the latter point to the Naturalization Act of 1790, which states that "the children of citizens of the United States … shall be considered as natural born citizens." The act adds an exception, which is that "the right of citizenship shall not descend to persons whose fathers have never been resident in the United States."

The Naturalization Act is the strongest argument for Cruz. Written in the immediate aftermath of the ratification of the Constitution, it was embraced by many people who were involved in drafting the founding document. (And because Rafael Cruz had resided in Texas, his son would count as natural born under the act.)

Yet the act isn't necessarily decisive. First, it governs citizenship generally, not qualifications for the presidency. Second, it says that the children of U.S. citizens "shall be considered as natural born citizens" — not that they are natural-born citizens. The Constitution's eligibility requirements, which Congress can't alter, might have meant to emphasize place of birth.

In any case, that act was repealed by the Naturalization Act of 1795, which somewhat mysteriously struck the term natural born and simply 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 citizens of the United States" (while retaining the same paternal residency restrictions as the 1790 act).

For technical reasons, no federal court is likely to rule against Cruz. First, it is settled that voters as such lack standing to sue, and there is a good chance that no one can establish the required "injury" to complain in court about Cruz' foreign birth. Second, the issue might be taken to present a "political question," in the technical sense that it will be treated as one to be resolved through the democratic process, not the judicial system. (Donald Trump suggests that Cruz should seek a declaratory judgment, but you can't go to court just because you are interested in its opinion.)

On the merits, I agree with Cruz: The Naturalization Act of 1790 counts in his favor, and because he was a U.S. citizen at birth under U.S. law, the better view is that he is natural born. But University of San Diego constitutional specialist Michael Ramsey, a former law clerk to Justice Antonin Scalia, put it well:

"It's a mystery to me why anyone thinks it's an easy question."

Cass Sunstein is director of the Harvard Law School's program on behavioral economics and public policy.