Story highlights Possible 2016 presidential candidate Ted Cruz's birth circumstances raise eligibility questions

Cruz was born in Canada to U.S. citizen mother and Cuban father

Birther-in-chief Donald Trump raised question of Cruz's eligibility in weekend appearance

Question hinges on the definition of what is a "natural-born" citizen

While the issue of President Barack Obama's birth has long been settled , and it's a moot point anyway since he's in his second term in office, there remain some people who won't be convinced.

Just ask members of Congress, who even this summer are encountering so-called "birthers" at town hall meetings.

With Ted Cruz, there is no conspiracy. He wasn't born in the United States. But that hasn't stopped the junior Texas senator from courting a possible presidential bid.

The dynamic young senator has traveled to Iowa and other early primary states. If his moves toward a candidacy become more serious, they're sure to spark first a debate about his conservative politics, but also that recurring debate about whether a "natural-born citizen" can be born outside the United States.

Birther-in-chief Donald Trump, who appeared to be running singularly on that issue in 2011, was more restrained when he was asked if Canadian-born Cruz was eligible to be president. "Perhaps not," Trump told ABC News on Sunday

"I don't know the circumstances. I heard somebody told me he was born in Canada. That's really his thing," said Trump, who could face Cruz in a GOP primary if both men follow through with runs they appear to be teasing.

Cruz seems to think the facts are on his side.

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"My mother was born in Wilmington, Delaware. She's a U.S. citizen, so I'm a U.S. citizen," Cruz told ABC in July . "I'm not going to engage in a legal debate. The facts are clear," he added. "I can tell you where I was born and who my parents were. And then as a legal matter, others can worry about that. I'm not going to engage."

There is precedent for people born outside the United States making credible runs for the presidency. George Romney, Mitt Romney's father, was born in Mexico to Mormon missionaries. He ran for president in 1968.

For all the ink spilled about Obama's provenance -- Hawaii, people -- it was actually John McCain in the 2008 presidential contest who was born outside the United States.

McCain's father, an admiral, was stationed in the Panama Canal Zone.

Democrats didn't make an issue of McCain's birthright to run, however. In fact, Democratic candidates Obama and then-Sen. Hillary Clinton sponsored a non-binding resolution in the spring of 2008 declaring that McCain was a natural-born citizen.

This is all the U.S. Constitution has to say about the qualifications to be president:

"No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President; neither shall any Person be eligible to that Office who shall not have attained to the Age of thirty five Years, and been fourteen Years a Resident within the United States."

That's pretty clear. Only a 35-year-old (or older) "natural-born citizen" can be president. But it turns out not be that clear.

Who is a "natural-born citizen?"

Citizen scholarship falls on the side of McCain. He had two American citizen parents and one was working for the U.S. government when he was born in Panama.

Cruz doesn't check all those boxes. His father, a preacher who has delivered stem-winding speeches of his own, has since become an American. But at the time of Ted's birth in Canada, he was a Cuban émigré working for an oil company. His mother, however, hails from Delaware.

There is a 50-page report prepared for lawmakers by the Congressional Research Service.

The key paragraph in that lawerly paper reads this way:

"The weight of legal and historical authority indicates that the term "natural born" citizen would mean a person who is entitled to U.S. citizenship "by birth" or "at birth," either by being born "in" the United States and under its jurisdiction, even those born to alien parents; by being born abroad to U.S. citizen-parents; or by being born in other situations meeting legal requirements for U.S. citizenship "at birth."

It does not specifically deal with the issue of someone born outside the United States to one American parent. But if Cruz could claim citizenship at birth, according to the argument, he could claim to be natural born.

The natural-born citizen requirement was put into the Constitution, according to the congressional report, to ward against aristocracy coming to America and setting up a new kingdom.

There has been discussion of doing away with the requirement altogether.

Sen. Orrin Hatch, R-Utah introduced the Equal Right to Govern Amendment in July 2003. It would allow immigrants who had been naturalized for at least 20 years to run for president. But it has gone exactly nowhere.