Technically, a U.S. "commonwealth."
Were both of Serrano’s parents US citizens at the time of his birth? What’s so hard about that?
Puerto Ricans are U.S. citizens from birth, but they were granted citizenship by statute, not by direct Constitutional grant of citizenship under the 14th Amendment. That is why there is an unresolved question as to whether someone born in Puerto Rico is eligible for the Presidency. Serrano asks Thomas that question every year, and that is why Thomas jokes about "evading" the question.
Prior to that exchange, was there a question(s) before the court regarding Puerto Ricans and weather or not they are eligible to be POTUS?
A statutory citizen can never be considered a “natural born” citizen.
A “natural born” citizen just is, and requires no statute, law or constitutional amendment to make him/her so.
ALL statutory citizens are born with a first generation tie to another nation by birthplace and/or blood, but NEVER is that the case with any natural born citizens who are only American.