Rumors are that he was so drunk that he was incapacitated. We might never know unless a tell all book gets released.
I don’t think drinking it his thing. I have zero doubt he was in no condition for duty. My guess is that he was doing the same thing he was doing before the first Romney debate. The one where he was missing for a while, showed up unexpectedly at the Roosevelt Dam when he was supposed to be prepping for the debate and then showed up at the debate disheveled, out of it and unprepared.