The clause in the US Constitution is brief and potentially ambiguous, but there has been no shortage of lawsuits about presidential eligibility and the legal definition in practice seems to be quite unambiguous.

For example, regarding Ted Cruz:

> Two November 2015 ballot challenges in New Hampshire alleging that Cruz was not a natural-born citizen were unsuccessful. In December, a similar lawsuit was filed in Vermont, and an unsuccessful lawsuit was filed in Florida. In January 2016, similar lawsuits were unsuccessfully filed in Texas and Utah, and two similar unsuccessful ballot challenges were filed in Illinois. In February, two similar unsuccessful lawsuits were filed in Pennsylvania and one was filed in Arkansas; a similar lawsuit was filed in Alabama; similar unsuccessful ballot challenges were filed in Indiana; and similar ballot challenges and an unsuccessful similar lawsuit were also filed in New York. In March, a similar lawsuit was filed in New York. In April, a similar ballot challenge was unsuccessfully filed in New Jersey.

> No lawsuit or challenge has been successful, and in February 2016, the Illinois Board of Elections ruled in Cruz's favor, stating, "The candidate is a natural born citizen by virtue of being born in Canada to his mother who was a U.S. citizen at the time of his birth."

https://en.wikipedia.org/wiki/Natural-born-citizen_clause#Te...

Which is, frankly, the sensible definition. People would and should rightly look askance at a court decision that found some obscure legal precedent to come to a different decision rather than just letting the voters decide. The question may make for interesting law review articles but there's pretty much zero practical justification for a more stringent definition. (Especially given that even the citizen from birth requirement is arguably something of an anachronism.)