Doug, my friend, no matter how much money you throw at our crack military and secret services you can't build a "fortress America" strong enough or smart enough to prevent things like this from happening. There are too many people in this world who, right or wrong, hate us and have nothing to lose. Marginalized people. People who see our wealth and privilege, and who we routinely choose to ignore or insult. People whose reality is hard enough that they consider blowing themselves up along with us to be an acceptable option. This is not as simple as "turning the other cheek". But neither is it time to return salt for salt, or any other cliche or religious bromide you want to toss around. We have to stop this madness.
But this is not the time to stir things up. This is a time to see to our injured and our dead. There will come a time when we will find out who did this and what we will do in turn. But if we don't take the time to try to consider why this was done, we will face this again. And no macho posturing will change that.