WHEN you’re behind in the polls, attack your opponent in some new and creative way. It’s a well-worn and occasionally effective strategy, and Donald Trump is employing it with aplomb against Ted Cruz in the last stretch of the run-up to the Iowa caucuses on February 1st. Last week, echoing old questions about the birthplace of Barack Obama, Mr Trump renewed his scepticism about Mr Cruz's very eligibility to be president. The billionaire White House aspirant noted that Mr Cruz was born in Canada to parents of mixed heritage: while his mother was an American citizen, his father was born in Cuba. “Republicans are going to have to ask themselves the question”, Mr Trump said, “do we want a candidate who could be tied up in court for two years? That’d be a big problem”. Article II of the Constitution mandates that a president must be at least 35 years old and “a natural born citizen”. Mr Trump is not certain that Mr Cruz is not a natural born citizen. In fact, he says that he hopes he is. “I’m doing this for the good of Ted”, he said. “We have a good relationship”. Mr Trump advises the senator from Texas to go to federal court and ask for a declarative judgment regarding his citizenship to put the issue to rest. Meanwhile, Mr Cruz is mocking his gadfly for resorting to a “silly circus sideshow”.

Thanks to an op-ed piece in the Los Angeles Times by Fordham law professor Thomas Lee and another op-ed from Harvard law professor Laurence Tribe in the Boston Globe, Mr Trump’s latest claim suddenly has scholarly support. He couldn’t be happier. The Guardian may have overstated things a bit in saying that Mr Tribe is “perhaps the most respected liberal law professor in the country”, but he’s certainly no lightweight. A month ago, Mr Tribe outlined the defects of Mr Trump’s plan to ban all Muslims from travelling to the US. Now, Mr Trump is hailing the professor as “a constitutional expert”.

To be clear, neither Mr Lee nor Mr Tribe believes Mr Cruz is ineligible for the presidency. Both scholars say, however, that strictly applying the interpretive theory known as “originalism” may lead a judge to question whether the circumstances of his birth fit the Article II standard. According to Mr Lee’s reading, the reigning view of natural-born citizenship at the founding held that in the case of a baby born outside the country’s borders, citizenship could be inherited only through the father. Since Mr Cruz’s father wasn’t an American citizen, baby Ted would, under the founders’ view, be Canadian, not American. Mr Tribe’s take is similar: under Mr Cruz’s favoured jurisprudential theory, he would be out of luck: "the kind of judge Cruz says he admires and would appoint to the Supreme Court is an 'originalist', one who claims to be bound by the narrowly historical meaning of the constitution’s terms at the time of their adoption. To his kind of judge, Cruz ironically wouldn’t be eligible, because the legal principles that prevailed in the 1780s and ’90s required that someone actually be born on US soil to be a 'natural born citizen".

These comments on Cruzgate from respected law professors represent an unfortunate intrusion into a Republican campaign season that has already been less than edifying. Fanning the flames of another birther critique—while carefully distancing themselves from the actual position—has a disingenuous feel. It is true, as Mr Tribe says, that “our Supreme Court has never addressed the issue”. But it’s one thing to say that the high court has not settled the question and other to egg on Mr Trump and stir doubt in voters' minds by saying the question is “unsettled”.

Neither Mr Tribe nor Mr Lee point to any actual judges whose originalist commitments would actually lead them to disqualify Mr Cruz from the presidency. The concern remains highly speculative. As Mr Tribe admits in his op-ed, "no real court is likely to keep Cruz off the ballot, much less remove him from the White House if he were to win". He then imagines a sequence of events in which Mr Cruz is elected president, appoints originalist jurists to the Supreme Court, and those very judges rule that since "he wasn’t a 'natural born citizen'" Mr Cruz "couldn’t exercise executive power against anybody". Sounds like a constitutional crisis, right? Wrong! The story is not remotely plausible. Mr Tribe acknowledges near the end of his article that "this almost farcical scenario would [not] be likely to unfold in reality".

Mr Tribe began his op-ed by claiming that there is "more than meets the eye" in the dispute over Mr Cruz's status as natural born citizen. As it happens, there's quite a bit less. Mr Tribe is just mocking his old student's favoured mode of constitutional interpretation: Mr Cruz could be hoist by his own petard, the Harvard scholar smirks, if he follows through on his principles. But the teacher quickly adds: this would never actually happen in the real world. In his back-handed critique, Mr Tribe inadvertently concedes to originalists one of the central virtues they hail for their theory: its capacity to yield a single clear understanding of each constitutional provision. But opponents of originalism rightly point out the difficulty of ascertaining the meaning of a constitutional phrase by simply asking how people construed the language during the founding era. There is often evidence of multiple understandings of a provision that lie in mutual tension, and originalists tend to resolve the matter by reading their own ideological views into the constitution.

A more responsible approach to the matter of natural born citizenship came last March from two former solicitors general of the United States, Paul Clement and Neal Katyal, who sought to dispel worries in the Harvard Law Review in hopes that “voters should be able to choose from all constitutionally eligible candidates, free from spurious arguments that a US citizen at birth is somehow not constitutionally eligible to serve as president simply because he was delivered at a hospital abroad”.

Messrs Clement and Katyal write that under no plausible understanding of “natural-born citizen” is there any doubt of Mr Cruz’s eligibility to serve as president. “Despite the happenstance of a birth across the border, there is no question that Senator Cruz has been a citizen from birth”, they argue. The only way to understand the founders’ view of “natural born citizen” is to consider how the British construed the term. "Laws in force in the 1700s recognized that children born outside of the British empire to subjects of the crown were subjects themselves and explicitly used ‘natural born’ to encompass such children”. These statutes provided that children born abroad to subjects of the British empire were “natural-born subjects . . . to all intents, constructions, and purposes whatsoever”. Since these laws were binding in the colonies in the 1770s, the Framers must have been “intimately familiar with these statutes and the way they used terms like ‘natural born’”. The definition is also found “in Blackstone’s Commentaries, “a text widely circulated and read by the framers and routinely invoked in interpreting the constitution”.

It’s no surprise that Mr Trump is undeterred by such pre-emptive articles in law journals: his newest charge has helped him edge in front of Mr Cruz in Iowa. Neither is it a shock that he is now hailing as one of the greatest living constitutional experts a scholar who just weeks ago picked apart the legality of his plan for Muslims. But it’s disappointing to see the professoriat prolong debate over yet another distraction in the presidential campaign just because they have a bone to pick with Mr Cruz about constitutional theory.