This whole unfortunate affair only underlines the resposibility of the Captain and the possible consequences of decisions taken by him. It would appear that incorrect paperwork began the events. Possibly attitude might have accacerbated the situation and a decision was taken.
The fact that a delay was incurred indicates that some effort was made to sort the problem out and it would seem not to have just been " he's and Arab I am not having him on board."
It is quite natural that POTUS would have to be indignant these people are his immediate bodyguard and anybody in that position would quite naturaly want to follow up.
It is also, I am glad to see proper for AA to back up the Captain. A full investigation will no doubt follow and the relative merits or shortcomings of the situation will be examined in detail. A decision on who was right or wrong will then be made. Once that is made and the full details are available we can all chew it over to our hearts content, in the meantime without all the facts opinions are just that, opinions.