Where Cruz was born is irrelevant, whether he is a US citizen is irrelevant – only thing relevant is the citizenship of his father at time he was born. His father was a Cuban citizen when Cruz was born. Under natural law principles, every individual must be a natural born citizen of one and only one country. Traditional rule is to go by father’s citizenship. If we used the mother’s citizenship, Cruz would be a natural born citizen of two nations and we just cannot have that when talking about the Presidency.