I think he's addressing it by his comments about not relenting. To do more is potentially disruptive to undecided voters. Let them think over the alternatives on their own.
I disagree. He's cast himself as a warrior against "terror", not just "American" terror. He has to directly address this. He has to publicly express his condolences and outrage at this news.
They raised the ante well over the bar, and there is no reason to believe these al Qaeda-trained terrorists will not have their actions copied here someday.