You don't really believe that only "senior operatives" are on any kind of watchlist, do you? We've caught lots of jihadis and gotten lots of info and names.
Sure, in places like Afganistan. If the terrorists want to train and find people to send into this country, they are smart enough to find people they can't identify. give the a little credit: 911 was a BRILLIANT plan, no matter how insidious. And, having let that cat out of the bag, they are not reverting to it. They are coming up with new ideas. But, they definitely have the resources not to be skulking into this country like peasants.