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.
One reasonable approach is to personally call President Putin and just listen. Remember, there is some history here. We haven't always supported the Russians against the Chechyens. This is a weird time to pipe up in public and say something. I agree that I would take great satisfaction about it if he did. But I think you simply have no idea how massive of a response the Russians are capable of doing all on their own. It may, in fact, be a good idea to just get out of their way.