Harvard law professor: Ted Cruz's eligibility to be president is 'murky and unsettled'

The legal and constitutional issues around qualification for the presidency on grounds of US citizenship are “murky and unsettled”, according to the scholar cited by Donald Trump in his recent attacks on Ted Cruz .

Related: Ted Cruz insists he is a natural-born citizen after new Donald Trump attack

Trump has sought to cast doubt on whether the senator, who was born in Canada to an American mother and a Cuban father, is a “natural-born US citizen”. In doing so he has referred to the work and words of Laurence Tribe , perhaps the most respected liberal law professor in the country.

Tribe taught both Cruz and Barack Obama at Harvard Law School. He also advised Al Gore in the 2000 Florida recount and has advised Obama’s campaign organisation.

“Despite Sen[ator] Cruz’s repeated statements that the legal/constitutional issues around whether he’s a natural-born citizen are clear and settled,” he told the Guardian by email, “the truth is that they’re murky and unsettled.”

Tribe has said previously that the question of Cruz’s eligibility is “unsettled”. On Sunday, Trump cited that position in an interview with NBC’s Meet the Press, in which he described Tribe “as a constitutional expert, one of the true experts”.

At a rally in Reno, Nevada later on Sunday, the real-estate billionaire, who has said Democrats will sue to stop Cruz running should he win the nomination, described himself as “a PhD in litigation”. Of Cruz’s eligibility, he said: “There is a doubt. We can’t have a doubt.”

Article II, section I, clause V of the US constitution states: “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.”

In his emails to the Guardian, Tribe discussed Cruz’s own approach to constitutional issues, noting that under “the kind of judge Cruz says he admires and would appoint to the supreme court – an ‘originalist’ who claims to be bound by the historical meaning of the constitution’s terms at the time of their adoption – Cruz wouldn’t be eligible because the legal principles that prevailed in the 1780s and 90s required that someone be born on US soil to be a ‘natural born’ citizen.”

He added: “Even having two US parents wouldn’t suffice for a genuine originalist. And having just an American mother, as Cruz did, would clearly have been insufficient at a time that made patrilineal descent decisive.

“On the other hand, to the kind of judge that I admire and Cruz abhors – a ‘living constitutionalist’ who believes that the constitution’s meaning evolves with the needs of the time – Cruz would ironically be eligible because it no longer makes sense to be bound by so narrow and strict a definition.”

Tribe said: “There is no single, settled answer. And our supreme court has never addressed the issue.”

Trump, who trails Cruz in polls in Iowa , first raised the issue last week. Cruz has since cited a bipartisan Harvard Law Review article by two former solicitor generals, Neal Katyal and Paul Clement, to back his contention that he is a natural-born citizen. Some of his rivals have pushed back ; the Kentucky senator and presidential rival Rand Paul and Arizona senator John McCain , the 2008 candidate, have declined to support him.

The former Massachusetts governor Mitt Romney, the Republican nominee in 2012, tweeted on Friday that Cruz was indeed a “natural-born citizen”.

Tribe, who became a hate figure to many on the right thanks to his role in derailing the supreme court nomination of Robert Bork in 1987, gave legal advice to McCain when similar “natural-born citizen” questions arose in 2008. McCain was born in the Panama Canal Zone, to two Americans.

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Working with Ted Olsen, a former solicitor general in the George W Bush administration, Tribe concluded: “[McCain’s] birth on a US military base within a territory controlled by the US from 1903 to 1979 … under a treaty with Panama probably (although not certainly) qualified him as a natural born citizen, especially because both his parents were US citizens at the time.”

On Sunday, he wrote: “That situation differed greatly from the one Sen[ator] Cruz finds himself in.”

Asked if he was surprised by Trump’s use of his name, Tribe wrote: “What I find surreal isn’t that a Republican presidential candidate would favorably cite my legal conclusions, but that anyone should find that phenomenon so shocking.

“The fact that I’m a lifelong liberal and a registered Democrat who taught constitutional law to President Obama (and, by the way, to Chief Justice Roberts and Senator Cruz) makes my citation by a likely Republican nominee for president surprising only because our political divisions have become so profound and so paralyzing that people no longer believe in the possibility of disinterested legal research.

“That’s really sad.”

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