I'm guessing the sheer volume of air travel in the US is one problem. Example: I travelled to Israel a couple of times for work. Their security is world clas

I'm guessing the sheer volume of air travel in the US is one problem. Example: I travelled to Israel a couple of times for work. Their security is world class, but they take a more predictive approach: having trained people interview all passengers even before checkin and look for subtle body language clues or inconsistencies, as well as your nationality/ethnicity/previous travel to gauge the level of risk. This is effective but it wouldn't be able to scale for a country as big as the US (300M vs 8M people); these are trained professionals, not folks that get paid a low hourly wage as is the case with the TSA.