Concerning Ted Cruz being a Natural Born Citizen or not, remember trump did not bring this up, he was asked a question by a reporter. Trump suggested that Cruz go to federal Court and get a ruling, I doubt that he will though.
At the time Cruz was born, his father was a citizen of Cuba, he was not an American citizen and Cruz inherited Cuban citizenship from him. In additionally, Cruz had a Canadian citizenship based on his birth in Canada, and it appears that his mother got Canadian citizenship as well. Congressman and candidate for Senate from Florida, Alan Grayson already announced that he will file a legal challenge against Cruz, should he become a nominee.
Rubio has the same problem, for at the time of his birth both of his parents were citizens of Cuba and did not have the US citizenship.
To understand the issue click here: