I wonder what he was reading about.
Another possible source of the clause is a July 25, 1787 letter from John Jay to George Washington, presiding officer of the Convention. Jay wrote:
“Permit me to hint whether it would not be wise and seasonable to provide a strong check to the admission of Foreigners into the administration of our national Government, and to declare expressly that the Command in Chief of the American army shall not be given to nor devolve on, any but a natural born Citizen.”