The real problem in this case wasn't the surveillance, it was that after flagging this guy, they could strip him of travel rights, i.e. air travel, but they did

The real problem in this case wasn't the surveillance, it was that after flagging this guy, they could strip him of travel rights, i.e. air travel, but they didn't have a means to deny him access to guns. The NRA have made it nearly impossible to deny anyone access to guns. It's harder to get a driving license. If they thought he was to great a risk to fly, he should have been too great a risk to buy and possess guns.