Sometimes, the targets are too easy. We've heard stories for years of problems with the security screening network in the US; now comes this:
Too, there's the problem of "fighting the last war". In this case, we have poured billions upon billions into securing the air traffic network. Why? Because 9/11 involved airplanes, and because it looks like it might be doable. But the two largest terrorist attacks/attempts on US soil prior to 9/11 both involved rental trucks (one directed at the World Trade Center, no less) - did we go after the rental truck industry? Then there are boats, problematic border crossings, and all the rest of it.
The fact is that terrorism is all about asymmetry, which makes guaranteed security impossible. Moreover, in the grand scheme of things terrorism ranks far behind murder, traffic accidents, and any number of health issues as a threat to American lives. Yes, it's more economically disruptive - to a point. But those disruptions are incredibly rare - indeed, vanishingly so in recent years.
For the most part, terrorism isn't much on the public radar these days. The presidential candidates have other things to talk about that are more attuned to Americans' concerns. And it isn't that we don't need some kind of response to terror threats, just as we need systems for dealing with natural disasters, auto accidents, murders, and a host of other problems. Here's hoping that this year's president campaign doesn't wander into the silly territory of pandering, wherein candidates promise us complete immunity from terrorists. Because there ain't no such thing.