Of course it was on purpose but he needs to not complain. It makes him look like he is making excuses, which makes him look weak and implies that he knows he lost. He just needs to do much much more prep for the next time and come out swinging harder.
In other words, yes he needs to prepare for the debates more than he did for this one. This one is okay though because it may have just made Hillary overly confident, and in the next one he can deliver the knockout punch.
Yes but, the Trump team should make sure it doesn't happen again. Perhaps force the debate to an outside sound stage with only a hard-wired feed to the outside world. That's my professional opinion. I rarely play the "Pro" card on FR, but this has been my life from the time I was a fifteen year old paid "teen-age" disk jockey. Had my first salaried job by 19, degree from Michigan State and Navy photo school.