Whether you think it’s a legitimate issue or not, Donald Trump has gotten everyone questioning whether Ted Cruz is eligible to serve as President of the United States based on the constitutional requirement that the president is a “natural born citizen.” Legal scholars write similarly convincing opposing arguments over how to define this constitutionally vague term. These are lengthy stories, but they’re both worth the read to fully grasp this issue. It will help you when you’re watching the debate later and this topic inevitably comes up.

Here are two views, both from constitutional law professors at respected universities, which differ on whether Ted Cruz is eligible under the constitution.

First, the opinion from Akhil Reed Amar, constitutional law professor at Yale University, who believes Cruz is eligible:

Elsewhere, Article I, section 5 of the Constitution makes clear that each house of Congress may “judge” whether a would-be member of that house meets the constitutional eligibility rules for that house. Suppose Mr. Smith wants to go to Washington as a senator. He wins election in his home state. But the Constitution says a senator must be 30 years old.

If a dispute arises about Smith’s age, about whether there a proper birth certificate and what it says, the Constitution clearly says the Senate is “the judge” of Smith’s birth certificate dispute.

Similarly, for presidential elections the Constitution’s structure makes Congress the judge of any birth certificate dispute or any other issue of presidential eligibility. Congress cannot fabricate new presidential eligibility rules but it is the judge of the eligibility rules prescribed in the Constitution.

Thus, ordinary courts should butt out, now and forever. They have no proper role here, because the Constitution itself makes Congress the special judge. In legal jargon, the issue is a “nonjusticiable political question.”

So the question is, was Ted Cruz born a citizen? The Constitution says, in the 14th Amendment, that anyone born in the United States and subject to our laws is a U.S. citizen. Today, that means everyone born on American soil except children of foreign diplomats — even children whose parents are not themselves U.S citizens. Donald Trump, are you listening?

Unlike Barack Obama, who was born in Hawaii — again, please pay attention, Donald! — Cruz is not a citizen at birth because of where he was born. Cruz was born in Canada. But neither Article II nor the 14th Amendment says that only those born in the United States are birth citizens. The 14th Amendment says that birth on American soil is sufficient to be a birth citizen. But it is not necessary. [Emphasis added]

How else can a person be a citizen at birth? Simple. From the founding to the present, Congress has enacted laws specifying that certain categories of foreign-born persons are citizens at birth. The earliest statute, passed in 1790, explicitly called certain foreign-born children of U.S. citizens “natural born citizens.” It did not say they should be treated “as if” they were “natural born citizens.” It said they were in law deemed and declared to be “natural born citizens.” Congressional laws have changed over the years, but this 1790 law makes clear that from the beginning, Congress by law has the power to define the outer boundaries of birth-citizenship by conferring citizenship at birth to various persons born outside the United States.

Amar’s argument boils down to the fact that congress ultimately is the legislative branch, and they determine what it means to be a citizen. In this case, current law made Cruz a citizen from birth. Therefore, Amar concludes, he is eligible to serve because congress, using the authority it has, deems him eligible.

Now, for the other side of this coin. Mary Brigid McManamon, constitutional law professor at Widener University’s Delaware Law School, takes an opposing view arguing that Cruz is not eligible to serve as president:

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. [Emphasis added]

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.

McManamon takes a very literal interpretation in that anyone who is born outside the United States, except for someone born on a US military base, cannot by definition be a “natural born citizen.” Therefore, barring a change to the constitution, Ted Cruz cannot be eligible regardless of what congress says or does with regard to granting citizenship.

There’s no doubt that Trump brought up the issue at this point out of political opportunism given the close race in Iowa. However, depending on who you ask, he’s not wrong for asking the question. How deep this topic gets explored at the debate tonight will be interesting to watch.