Sen. Ted Cruz (R-Tex.) speaks during the GOP primary debate on October 28, 2015 at the University of Colorado in Boulder. (ROBYN BECK/AFP/Getty Images)

Sen. Ted Cruz (R-Tex.) was born in Canada to an American mother and a Cuban father. Can he constitutionally run for president?

Actually, the Constitution is a bit fuzzy on this question, and you can find a lot of people with a lot of different opinions about it. For example, Donald Trump, Cruz's biggest rival in the GOP presidential primary, thinks the answer might be no.

It all depends on what you think the phrase "a natural born Citizen" means -- which, the Constitution states, is what you have to be if you want to run for president. It's an ambiguous term, and reasonable people disagree on how to interpret ambiguous language in the country's founding document.

Many legal scholars say Cruz qualifies, and while it has become a political flash point, it still seems pretty unlikely it becomes an actual legal barrier to Cruz moving forward with the campaign.

Interestingly, though, some legal experts say that if you subscribe to Cruz's own principles of constitutional interpretation, he might not be eligible. And for reasons that have a lot to do with gender norms of the 18th century.

Many legal scholars say Cruz supports an approach to constitutional law in which modern readers try to understand what the words in the Constitution would have meant to the people who wrote them and voted to ratify them more than two centuries ago. It's a concept known as originalism, and it's especially popular with conservatives.

"It’s not: take what part you like and get rid of the parts you don’t like," Cruz said in 2013. "Every word of the Constitution matters."

On this straightforward, intuitive, and deeply conservative reasoning, several prominent legal scholars have argued Cruz is arguably not a natural-born citizen. As the Founding Fathers and their contemporaries probably would have understood that phrase, the argument goes, Cruz is ineligible for the presidency — not because he was born in Canada, but because he was born in Canada to a Cuban father.

"He should disqualify himself," said Thomas Lee, a legal scholar at Fordham University, adding that Cruz should "just be consistent."

Lee explains that in medieval English law, the term "natural born" originally referred to subjects of the crown who were born in English territory.

Under King Edward III, who reigned from 1327 to 1377, England expanded this definition to include the children of ambassadors and soldiers who were serving the monarch overseas. In the centuries to come, Parliament modified the definition further to include the children of private English subjects who happened to be abroad.

In the late 18th century, though, that definition did not include English mothers who were traveling. If they conceived children with foreign men, it was assumed those children would not be loyal English subjects and were not considered "natural born."

"We don't understand how sexist society was back then," Lee said. "They thought that you got your blood, your politics, your loyalty, your allegiance from your father. The mother was irrelevant."

Many Americans object to the notion we must follow the original implications of the words in the Constitution with regard to gender. Many legal scholars argue that the meaning of the document changes with time, along with the mores and values that shape American society and determine how Americans of any given era will make sense of the Constitution's text.

On this view, according to which the Constitution is an evolving, living document, it's not as important how the Founding Fathers thought about children's relationships with their fathers and mothers. Americans today are free to apply their own ideas about gender and family to the text of the Constitution.

Yet as Cruz sees it, a truly conservative reader of the Constitution does not reject the original meaning of the text simply because it offends the modern sensibility or because it's politically convenient to do so. Following the Supreme Court's ruling in favor of the right to marry for gay and lesbian couples last summer, Cruz accused the justices of "rewriting the Constitution."

In any case, at the time that document was ratified in 1788, Lee has argued that the phrase "natural born" would have carried a specific legal meaning. Natural-born citizens would have been those born in the United States, or born abroad to fathers who were U.S. citizens. On that interpretation, Cruz would not have qualified because his mother was a citizen and his father was not. If Cruz takes an originalist approach to constitutional law, then by this logic, he should come to the conclusion that he is not natural born.

A spokesman for Cruz declined to comment for this story.

[Read more: Ted Cruz is not eligible to be president]

Some constitutional originalists disagree with this view, including Michael Ramsey of the University of California, San Diego. He has argued that just as Parliament in London had the power to change the definition of "natural born" for purposes of English law, the newly established Congress here in Washington D.C. could change what the phrase meant for American citizens.

In 1790, members of the first Congress took their seats and passed a law stating that as long as their fathers had lived in the United States for at least some time, children born overseas to American mothers "shall be considered as natural born." This was a law intended to spell out the new nation's immigration policy. It is not clear whether Congress also wanted to give a new meaning to the words "natural born" in the Constitution regarding would-be presidential candidates.

Under this definition, Cruz would seem to qualify, since his father had lived in the United States for years before Cruz's birth in Canada.

Lee and Ramsey have collaborated on legal projects in the past, but in this debate, they've parted ways.

Lee says it's "absurd" for an originalist to argue that Congress would have the power to change the meaning of words in the Constitution. According to Ramsey, though, there's no contradiction in assuming that lawmakers have this power. The authors of the Constitution allowed Congress to define "natural born Citizen" when they wrote that the legislature had the authority "to establish a uniform Rule of Naturalization," he says.

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)