The TSA's measures are worse than useless: they actually create a hazard, with long, slow-moving, densely-packed lines full of by-definition unscreened persons--lines that are about the ripest target for a bomb that you can find.
I've been thinking about that for years, but never said anything because I didn't want to give anyone any ideas.
People already have the idea and are making drama out of it. In Iain Banks' Transition, a Christian terrorist blows up a packed security line at the airport while guards up ahead are trying to take some nail clippers off a granny.
But while it's undefended right now, and you're at risk from it, it's not a threat the US needs to guard against, because no Islamists have tried it yet.
You can commit any act of terrorism in the US you like, it won't matter unless you're an Islamist, which is to say you have a beard and a funny hat. You can shoot up your local mall or campus, and that'll just be "a tragedy" and it will be forgotten by the next day, nobody will do anything about it. But if the TV reports a Mooslim even thought about blowing something up, the nation collectively loses its shit, so Something Gets Done, right there and then, no matter how hilariously improbable.
So, why don't Mooslims attack the US? Because most of them aren't terrorists, and the handful that are are either satisfied with what they've wrought so far (remember that Osama achieved his main goal of getting the US military out of Saudi Arabia, he only has one goal left - getting the US money out of Israel), or they're still scratching their heads as to how up the ante after 9/11. Tough job, and it will have to involve getting on a plane with a bomb, because that's what the US public are focused on and fear most.
Terrorists don't score points just on how many people they kill - they could just do a coordinated rampage in some shopping malls to top the 9/11 hiscore - but they score points on how spectacular and audacious their successful plots are. We're still fixated on exploding or hijacked transit, so that's what they have to aim for.
In Israel, however, the terrorists have lower standards. They'd get nationwide media coverage for killing any Israelis at all, so the murderous bastards are everywhere. Left the back door open? BOOM! Didn't eat your greens? BOOM! Terrorist hiding under the broccoli.
When you have a real threat, from groups who will accept any amount of death as a success, not just Bond movie plots, then you need to be far more focused. The US doesn't have a real threat, so it can keep deluding itself with security theater.
