Trump is clutching at straws, hoping he can get away with believing the implausible pack of lies offered by the KSA. Why? because of the effect on jobs of a stoppage of US arms sales.
I think it goes far deeper than that - the arms sales are on nothing like the scale he claims ($12.5 billion, nowhere near 110+ except over several decades), but his whole plan for the Middle East centres around KSA, whereas previous administrations had far more balanced plans.
You, like many others including the media, have also missed the crucial point:
MbS hasn't given "
an implausible pack of lies" - all he's said so far is "
I know nothing". While that may well be a lie, and even arguably an implausable one, all the "
implausible pack of lies" can with at least a veneer of plausibility be put down to the Consul and the "
rogue killers".
ETA today's news is that Kashoggi was dismembered, while still alive, on the consul-general's desk.
Headline grabbing, but contrary to all other reports and leaks and extremely unlikely as the bonesaw supposedly used was still in KSA. It does, however, play straight into Trump / MbS's hands (and they're pretty well interdependent and a mutual appreciation society.)
MbS now holds all the cards, openly backed by Trump. He's got all the players, literally, and it's for him to lose.
He can either brazen it out about the "
rogue killers", now including the Consular staff, and 'purge' the lot plus any others for good measure, making the most of the opportunity, and all the groundwork for that's been laid, or he can blow it completely by being arrogant enough to say that all they did wrong was kill Khashoggi by accident.
There's always the possibility of a coup, but other than that it really is MbS's to lose.