This could play out one of two ways. The first which Dave mentioned is a brokered deal in which Saudi Arabia is willing to no longer help groups like Isis and the US is willing to give arms in return. The second and historical precedent is that arms go to Saudi Arabia and wind up in the hands of groups like Isis. Seeing that Isis is having troubles in Syria this could be a shot in the arm if arms are given to them. Once the arms are delivered the US cannot control where they go. We will have to see how this plays out.