He is trying to pretend that they accessed the data for noble reasons and not taking advantage of the breach while it lasted when that obviously seems to be the case. They did something wrong but the problem here is that the DNC's response is heavy handed and unfair.
If this guy wants to help the campaign (which he obviously still do) he should stop giving more interviews.
How so? It seemed completely fair to me - yes, he pushed the staffer a bit but would there have been a point to the interview if he hadn't?
I'm not quite sure if I believe the Sanders campaign story, but that seems independent from the quality of the interview; even if you do, it shouldn't be a bad thing to ask more questions of individuals involved.
Push him on it, sure. After the 5th time of accusing him of stealing the data it felt a bit more like badgering the same point.
I think there are certainly some parallels as mentioned by the parent of the what constitutes a understanding of a breach vs ethics of accessing a system.