I think andrasz's summary is the one I go for, although I do think the BAC of 0.6 was relevant as it may have clouded judgement. Perhaps sober he may have realised that what was happening was not sensible.
Regarding cause 2), ANY VIP flight with a need to 'land' at a particular airfield at a particular time will ALWAYS create a pressure that 'normal' pilots do not understand and which requires a particularly strong discipline to resist. For historic reasons this Captain's 'strength' was affected. As I said way, back, a tragic and unnecessary loss of life - but then, are they all not?.