I would be interested in where Cruz was asked to name someone? You make the claim that he couldn't name someone, then would you be so kind to show where the question was even floated?
If this helps, here is the debate section in question. I don't see the question being posed at all, but perhaps you know something I don't (not that I am holding my breath).
https://www.youtube.com/watch?v=j16uMJxgCZU
Trump didn’t have to be asked a question. The subject came up and he had a couple of names ready. I guess Cruz and the ready didn’t.