Aside from being a "journalist", Khashoggi appears to be a member and proponent of the Muslim Brotherhood, which is at odds with the Saudis, and is hardly a step up from Wahhabism (which MBS seems willing to reign in). This looks like intramural squabbling within the House of Saud, which is not unsual, just unusually public in this case. I don't see any reason to for the US to get its knickers in a twist, unless one wants to sabotage the cooperation of the US, KSA, and Israel in opposing Iran, and pump up the influence of islamist Turkey and its dictator.