Cruz’s eligibility was at least questionable before Obama. Obama set the precedent. the natural born Constitutional requirement just means born of the union of an ovum with a sperm. And, who knows? perhaps even that requirement will be circumvented.
I don't think there is any reason to question Cruz's eligibility, Obama or not. Under the laws in place at the time of his birth Cruz is a natural born citizen, always has been and always will be.