Rafael (Ted) Cruz, the Alberta-born darling of the Republican right, a Tea Party favourite and brilliant legal scholar, finds himself in the vortex of a "birther" brouhaha over whether he meets the constitutional requirement that he is a "natural-born" citizen if he seeks to be president.

Senator Cruz, a Texan, has renounced his Canadian citizenship and insists he's a red-blooded American fully eligible to be president.

For the angry chorus on the far-right fringes of the U.S. political spectrum, a full-throated "birther" controversy was more fun when the target was Barack Obama, a Democrat and African-American with a Muslim father from Kenya and a Muslim stepfather from Indonesia.

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Now it's Mr. Cruz, with a Cuban father and a Canadian birthplace, who's being targeted; and some of his accusers are fellow Republicans, led by Donald Trump, the bombastic billionaire.

Mr. Cruz's eligibility is only the latest in a long series of "natural-born citizen" controversies dating back more than a century to Chester Arthur, another Republican who may have been born in Canada, and including the Mexican-born Governor George Romney and Arizona Senator John McCain, who was born in Panama.

Here is a review of presidential place-of-birth controversies, which picked up the shorthand "birther" when Mr. Obama first ran.

What the Constitution says

Very little. Article 2, Section 1, Clause 5 sets out three requirements for an individual to be eligible to be president or vice-president of the United States. A person must be 35 years old or older, a resident for 14 years and a "natural born Citizen." That crucial phrase is never explained, nor elsewhere repeated in the Constitution. It has never been adjudicated by the Supreme Court as to what it means or what the original framers meant when they wrote it. But debate swirling around the meaning dates back centuries.

What Ted Cruz says

"The facts and the law here are really quite clear. Under long-standing U.S. law, the child of a U.S. citizen born abroad is a natural-born citizen," Mr. Cruz insists, asserting he is eligible as the son of a U.S. citizen, his mother, who was born in Delaware. "If a soldier has a child abroad, that child is a natural-born citizen. That's why John McCain, even though he was born in Panama, was eligible to run for president. If an American missionary has a child abroad, that child is a natural-born citizen. That's why George Romney, Mitt's dad, was eligible to run for president, even though he was born in Mexico," he adds, referring to two notable previous Republican presidential candidates.

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"At the end of the day, the legal issue is quite straightforward," Mr. Cruz claims.

Not so much.

There are widely varying legal opinions, sometimes reflecting the legal and political biases of the authors. For instance, Laurence Tribe, a Harvard University constitutional expert, just wrote an article suggesting his former star student, Mr. Cruz, may not meet the framers' test under Mr. Cruz's own "originalist" approach to the Constitution. "At least he was consistent in those days," Prof. Tribe writes. "Now, [Mr. Cruz] seems to be a fair weather originalist, abandoning that method's narrow constraints when it suits his ambition." In response, Mr. Cruz points out that Mr. Tribe, an acknowledged liberal, was also lead counsel to Democratic presidential nominee and former vice-president Al Gore in his failed Supreme Court challenge to George W. Bush's presidential election win in 2000.

Who gets to decide?

The Supreme Court is the final authority as to what the Constitution means, and it won't consider the issue until and unless someone challenges the eligibility of a candidate. Despite lots of talk, no one ever has filed a legal challenge on the meaning of a "natural-born citizen" that has reached the Supreme Court.

Despite the controversy in the court of public opinion, as Prof. Tribe concedes: "No real court is likely to keep Cruz off the ballot, much less remove him from the White House if he were to win."

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If Mr. Cruz survives the birther fuss, is selected the Republican nominee, wins the election in November and is inaugurated a year from now, he could actually be the second Canadian-born president of the United States.

The Arthur conundrum

By one version in a murky and much-disputed history, Chester Arthur, the 21st U.S. president, was born in Canada. His father, William Arthur, an Irishman and itinerant minister was teaching in Dunham, Que., when he met Malvina Stone, a U.S. citizen from Vermont. They married, and Chester, their second child, was born in 1829 (or 1830) either in Fairfield, Vt., or near Bedford, Que., about 25 kilometres north of the U.S. border. Chester Arthur became a New York lawyer and a prominent Republican, and was selected by James Garfield as his running mate in 1880. Democrats seeking to discredit Mr. Arthur said he was born in Canada.

One A.P. Hinman claimed he had been hired by the Democratic National Committee to find evidence of Mr. Arthur's Canadian birth on the grounds that it would disqualify him. The whispering campaign failed, the Republicans narrowly won the 1880 election and Mr. Garfield became president. Six months later, Mr. Garfield was assassinated and vice-president Arthur succeeded him. To prevent Mr. Arthur from running again, Mr. Hinman published How a British Subject Became President. Canadian-born or not, Mr. Arthur knew he was dying and retired in 1884 rather than run for re-election. But the controversy still swirls in small towns on both sides of the Quebec-Vermont border and Mr. Arthur, at least, evidently believed a birth abroad might have been ruinous to his political fortunes. He lied about the year of his birth throughout his life, making it a year later when the family was clearly settled in Vermont.

Two opposing views on what "natural born" means

Mr. Cruz may assert that the matter is settled law, but it isn't. There are two very different interpretations.

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In one, "natural born" means the child must be born on U.S. sovereign territory. Anyone born in the United States, even if both parents are unlawfully in the country, is a citizen. Under that interpretation, those born both outside the United States even to U.S. citizen parents, are citizens from birth but not "natural-born" citizens and thus ineligible for the office of president or vice-president. That view, its advocates claim, more reasonably reflects the likely intent of the framers of the Constitution, who were writing at a time when no adult had been born in the United States since the country had only just declared its independence. Hence the wording: "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."

The opposing view, which seemed to be accepted until the birther controversy erupted over Mr. Obama's birthplace and citizenship, held that any U.S. citizen who was a citizen from birth – in other words had no need to apply for naturalization – was eligible.

Under that view, there was no bar to presidential eligibility for George Romney, the son of missionaries who were U.S. citizens living in the Mormon colony of Colonia Dublan in Chihuahua, Mexico, at the time of his birth in 1907. In 1968, Mr. Romney, by then governor of Michigan, was the early front-runner as Republican presidential nominee but eventually was beaten by Richard Nixon who was elected president.

Four decades later, the 2008 Republican nominee was also born abroad. John McCain, a decorated Vietnam war veteran and long-serving Republican senator for Arizona was born in 1936 in a U.S. military hospital in the Panama Canal Zone, then leased (as Guantanamo Bay, Cuba, is today) to the United States. But it was not sovereign territory and Mr. McCain's citizenship from birth was based on the citizenship of his parents, one a U.S. admiral, not geography.

But just to be sure, the U.S. Senate passed a resolution in 2008, sponsored by, among others, then-Illinois senator Barack Obama, which said: "Whereas John Sidney McCain, III, was born to American citizens on an American military base in the Panama Canal Zone in 1936: … therefore, John Sidney McCain, III, is a natural born Citizen under Article II, Section 1, of the Constitution of the United States."

No one seriously questioned Mr. McCain's eligibility, but Mr. Obama's was soon under attack, even though he was born in Hawaii to a mother who was a U.S. citizen.

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The campaign, known at the "birther" movement and fuelled by right-wing talk radio, claimed Mr. Obama, the son of a Kenyan Muslim, had lied about his birthplace, was really born in Kenya and thus, the citizenship of his mother notwithstanding, not eligible to be president. Mr. Trump, the New York property magnate currently questioning whether Mr. Cruz's birth in Calgary makes him ineligible to be president, was a leading player in the birther campaign about Mr. Obama. At one point, Mr. Trump offered a multimillion-dollar reward for Mr. Obama's birth certificate.

The facts of Rafael Edward Cruz's birth

On Dec. 31, 1970, the Alberta Division of Vital Statistics recorded the birth, nine days earlier, of a male named Rafael Edward Cruz, born to Rafael Bienvenido Cruz, a Cuban citizen, and Eleanor Elizabeth Wilson, a U.S. citizen. At birth, the boy thus held Canadian, U.S. and, probably, Cuban citizenship as his father didn't become a U.S. citizen until 2005. The couple was working in Alberta's oil patch and didn't move back to the United States until their Canadian-born son was four years old. The boy got his first U.S. passport when he was in high school and claimed in 2014 that he was unaware that he held Canadian citizenship. He formally renounced it, filling out the forms and paying the fees in 2014. All that accomplished was to end Mr. Cruz's dual Canadian-U.S. citizenship, an issue not raised in the Constitution.

What the research shows

Perhaps the least-partisan interpretation comes from the Congressional Research Service which, in 2011, published a paper on the issue. It concluded, "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.'"