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.

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. ...