Interesting article from the Harvard Law Review that goes through the history of the term "natural born citizen". The conclusion is that there is no issue and that there is no constitutional question.

All the sources routinely used to interpret the Constitution confirm that the phrase “natural born Citizen” has a specific meaning: namely, someone who was a U.S. citizen at birth with no need to go through a naturalization proceeding at some later time.
http://harvardlawreview.org/2015/03/...-born-citizen/