As to the President's security:
In retrospect, ChiefKujo should not have posted until POTUS was wheels' up. I'm sure the Chief was excited, but the keywords gave the game away and was a breach of security. Let's try not to let the cat out of the bag about the Chief, since CID and the Secret Service might want to bust him down to corporal. As it was, he posted while the President was on the ground, and in theory that might have made things easier for Mustafa the Mortarman.
In theory. I suspect that it might not have mattered. There were Apaches up all over the airport looking for heat signatures on the ground (a STRELA team would give off a nice heat sig). AF-1 landed at night to mask the President's arrival AND to allow the Apaches a clear shot at a heat signature. I also suspect that Sanchez made sure that a battalion of infantry were screening the airport perimiter, wondering what for of course, but probably told to be on the lookout for RPG and STRELA teams.
But all it takes is one lucky shot. So it is not our call to determine whether the President is absolutely safe, or not.
Be Seeing You,
Chris