You give an interesting story from a book and conclude that "I guess it's part of the job of the President to act angry [and emptily gesture a response or retaliation when things like this happen]". I disagree and think that it's part of the job of the President to actually be angry when something like today happens, and to make those who dare bring violence and death to one of us, see those actions answered, swiftly, and with prejudice, because to act otherwise is a moral hazard.
Obviously there is calculus that needs to be done (e.g. this situation, which seems a slam dunk, versus, say, responding to Russia or China who can and will make life very painful for us), but it would appear changing course briefly to exterminate those too dumb to immediately hide after this sucker punch, a bunch of idiots who couldn't help themselves and hold their water until we were out the door and out of earshot, seems like a low calorie effort comparatively.