Sen. Ted Cruz speaks with his wife, Heidi, by his side during a primary night campaign event in Indianapolis. Cruz ended his presidential campaign, eliminating the biggest impediment to Donald Trump’s march to the Republican nomination.

May 3, 2016 Sen. Ted Cruz speaks with his wife, Heidi, by his side during a primary night campaign event in Indianapolis. Cruz ended his presidential campaign, eliminating the biggest impediment to Donald Trump’s march to the Republican nomination. Darron Cummings/AP

Mary Brigid McManamon is a constitutional law professor at Widener University’s Delaware Law School.

Donald Trump is actually right about something: Sen. Ted Cruz (R-Tex.) is not a natural-born citizen and therefore is not eligible to be president or vice president of the United States.

The Constitution provides that “No person except a natural born Citizen . . . shall be eligible to the Office of President.” The concept of “natural born” comes from common law, and it is that law the Supreme Court has said we must turn to for the concept’s definition. On this subject, common law is clear and unambiguous. The 18th-century English jurist William Blackstone, the preeminent authority on it, declared natural-born citizens are “such as are born within the dominions of the crown of England,” while aliens are “such as are born out of it.” The key to this division is the assumption of allegiance to one’s country of birth. The Americans who drafted the Constitution adopted this principle for the United States. James Madison, known as the “father of the Constitution,” stated, “It is an established maxim that birth is a criterion of allegiance. . . . [And] place is the most certain criterion; it is what applies in the United States.”

Cruz is, of course, a U.S. citizen. As he was born in Canada, he is not natural-born. His mother, however, is an American, and Congress has provided by statute for the naturalization of children born abroad to citizens. Because of the senator’s parentage, he did not have to follow the lengthy naturalization process that aliens without American parents must undergo. Instead, Cruz was naturalized at birth. This provision has not always been available. For example, there were several decades in the 19th century when children of Americans born abroad were not given automatic naturalization.

[Opinion: Yes, Ted Cruz is a “natural-born citizen”]

Some of the Republican presidential candidates are going after Sen. Ted Cruz (R-Tex.), saying his birthplace could count against him in a presidential election. Here are the facts. (Sarah Parnass/The Washington Post)

Article I of the Constitution grants Congress the power to naturalize an alien — that is, Congress may remove an alien’s legal disabilities, such as not being allowed to vote. But Article II of the Constitution expressly adopts the legal status of the natural-born citizen and requires that a president possess that status. However we feel about allowing naturalized immigrants to reach for the stars, the Constitution must be amended before one of them can attain the office of president. Congress simply does not have the power to convert someone born outside the United States into a natural-born citizen.

Let me be clear: I am not a so-called birther. I am a legal historian. President Obama is without question eligible for the office he serves. The distinction between the president and Cruz is simple: The president was born within the United States, and the senator was born outside of it. That is a distinction with a difference.

In this election cycle, numerous pundits have declared that Cruz is eligible to be president. They rely on a supposed consensus among legal experts. This notion appears to emanate largely from a recent comment in the Harvard Law Review Forum by former solicitors general Neal Katyal and Paul Clement. In trying to put the question of who is a natural-born citizen to rest, however, the authors misunderstand, misapply and ignore the relevant law.

First, although Katyal and Clement correctly declare that the Supreme Court has recognized that common law is useful to explain constitutional terms, they ignore that law. Instead, they rely on three radical 18th-century British statutes. While it is understandable for a layperson to make such a mistake, it is unforgivable for two lawyers of such experience to equate the common law with statutory law. The common law was unequivocal: Natural-born subjects had to be born in English territory. The then-new statutes were a revolutionary departure from that law.

[Opinion: Trump’s bogus birther attack on Ted Cruz]

Second, the authors appropriately ask the question whether the Constitution includes the common-law definition or the statutory approach. But they fail to examine any U.S. sources for the answer. Instead, Katyal and Clement refer to the brand-new British statutes as part of a “longstanding tradition” and conclude that the framers followed that law because they “would have been intimately familiar with these statutes.” But when one reviews all the relevant American writings of the early period, including congressional debates, well-respected treatises and Supreme Court precedent, it becomes clear that the common-law definition was accepted in the United States, not the newfangled British statutory approach.

Third, Katyal and Clement put much weight on the first U.S. naturalization statute, enacted in 1790. Because it contains the phrase “natural born,” they infer that such citizens must include children born abroad to American parents. The first Congress, however, had no such intent. The debates on the matter reveal that the congressmen were aware that such children were not citizens and had to be naturalized; hence, Congress enacted a statute to provide for them. Moreover, that statute did not say the children were natural born, only that they should “be considered as” such. Finally, as soon as Madison, then a member of Congress, was assigned to redraft the statute in 1795, he deleted the phrase “natural born,” and it has never reappeared in a naturalization statute.

When discussing the meaning of a constitutional term, it is important to go beyond secondary sources and look to the law itself. And on this issue, the law is clear: The framers of the Constitution required the president of the United States to be born in the United States.