So, having now seen this guy working [to defend someone undefensible in the senate? I just don't see how he managed through law school in the first place.
Yes, I refreshed my memory about him, and his opening for the defence was pretty universally panned as meandering and empty of content (Trump wasn't happy about it, either, and had the other lawyers do most of the rest).
I've been trying to think what possessed him to act as he did, and my most charitable explanation is that, as an elected DA (and one who had his difficulties with the local party, I believe) he found himself confronted with a dilemma.
If he went ahead and prosecuted, he'd be criticised on all sides when, as almost certainly they would have done, the jury acquitted Cosby, both by people who thought he didn't do a good enough job and by people who didn't think the prosecution should have been brought.
However, if he didn't prosecute, he'd be criticised for letting Cosby get away with it.
So, solve the problem by forcing Cosby to give evidence on oath in the civil trial, which establishes what he did, and what he is, and getting his victim some compensation -- not ideal, but no one group of voters gets too mad with him.
As I say, there are less charitable explanations, but it's one way to understand why he'd have taken such a bad decision, because elections are a powerful disincentive to prosecute high-profile cases that have a scant chance of success.