I think the TSA has switched strategies recently, and they've been improving since then. But ultimately, its not the "bag check" where the TSA catches goons, its the random more intense check that they do these days. And sure, going from 95% failure to 80% failure isn't much of an improvement, but its still going to change the calculus of an attacker. When you have a 20% chance of failure before you even board the airplane, that's an issue to your plans.
Furthermore, TSA includes air marshals and the Israeli-style "behavioral" cops who are scanning airports. These are the more successful cops at the job, and the ones we are relying upon for real.
I wouldn't discount the entirety of the TSA just because of the failures of the bag-check program. Again, US Air marshals (armed cops who sit on every aircraft secretly with plain-clothes) are under the TSA and I think the US Air Marshals contributes a LOT to our real security.
Unfortunately, the bag-check thing is mostly security theater, but at the same time, the more "serious" checks vs attackers are more hidden and less well known (as it should be). But security theater might be enough to discourage an attack, or at very least cause our enemies to focus on the bag-check (when our REAL security really lies with other programs). So its a useful distraction IMO. There's a bit of "wink-wink lets not talk about this" going on that you need to understand though.
Bag check programs are focal to these discussions because they cause the most inconvenience to passengers.
Do they really sit on every flight?
https://aviation.stackexchange.com/questions/13264/are-air-m...
Once we got in the terminal he kinda flashed his ankle holster and told us to have fun on our vacation. Also mentioned something along the lines that we had made a normally boring 5 hour flight entertaining.
I should add this was 10+ years ago.
Btw, how did you recognize he was a FAM ?
I'll never forget one TSA agent who accusatorially said he didn't think I was purposely trying to break the law because it was engraved.
Don't even get me started how often my wife gets 'flagged' for extra security.
From my understanding they completed their part of the contract and never heard anything else about it.
I'd love to be proven wrong, though.
The main practical impediment to detecting concealed explosive material is that some of the explosive substance needs to pass through the GC-MS to be detected. So an explosive with extremely low vapor pressure (e.g. pure PETN) will not be readily detected this way. Plastic explosives made from PETN are more readily detectable, because the plasticizers are more volatile than PETN itself. GC-MS also won't work if the explosive is hermetically sealed so that none of it can reach the detector.
There are also methods based on e.g. terahertz spectroscopy, but AFAIK GC-MS is the most specific and common method of identifying explosive materials.