There is no case because the Enquirer is only reporting this as a rumor, not fact. Somehow, that fact has gotten lost by those eager to smear Cruz.
Cruz does himself a disservice by deflecting rather than denying.
Attacking his accusers and characterizing the accusation as a smear rather than directly denying the accusation is deflection. A denial would be, “I have not had extra-marital affairs”. It’s a clear unambiguous declaratory sentence with no wiggle room, it’s either true or false.
In my opinion he has not handled this well.