I agree with this part of what you said. Hopefully now that Trump has branded Carson as "pathological" he can back off on the personal stuff. I think he was doing fine before when he was contrasting his advantage in negotiating and dealing with people.
As for Levin, I think he was still pissed off from the other day when Trump tweeted about Carson lying (the Politico story), so this added to it.
I have only listened to half of the speech so far, but the part I have heard is not a "very bad" speech, quite the contrary. The section where he was discussing what the penalties are for illegally crossing other countries' borders was very strong. The part where he said he would "bomb the s__t out of ISIS" looks absolutely prescient given today's events.
Of course the only thing that anyone wants to remember is the Carson stuff, but that was 10% of it.
As others have said, Cruz is obviously Levin's guy if only because he is one of the few candidates with the right position in immigration. I don't necessarily see anything wrong with that, Levin gave both Trump and Rubio airtime this week and asked them both penetrating questions without being confrontational about it.
Mark defended Trump this week against people who were saying that Trump wasn't conservative enough.
And now a day or two later we have some Trump supporters trashing Mark.
Go figure.