Good for the Comair captain, he had the prerogative and he took it, the diplomat went on a latter flight (not much latter) with a crew that was more comfortable flying him and his ilk. The Comair captain will likely be required to justify his decision, which is appropriate. However, because of the nature of the situation, with high-level dignitaries involved, he may receive quite an admonishment. From a safety standpoint he made the right call, he was troubled with the situation and he exercised his authority. It would be very easy in this situation, with pressure from company, dignitaries (Do you know who I am? young man), and the State Department, to be obsequious and just take the flight.
Perhaps next time the dignitary will demand that you fly through a thunderstorm because he must get to his highbrow meeting. No, the precedent has been set – the captain is the final authority on the aircraft.