Isn't it MIND-BOGGLING? It all seems so straightforward.
Bad guys can waltz into the country - UNDETECTED. Many of them can easily get their hands on all sorts of nasty stuff (WMD included). They want to kill us - by the millions, if possible.
We spend BILLIONS playing defense. Have implemented this totally funky "alert" system that confuses everyone except the terrorists. We pour money into trying to lock down every square inch of the country EXCEPT the borders, that let the bad guys in in the first place!
Gee..HERE's a thought. Go round up the bad guys, like we did with the German spies in WWII that were sent here by Hitler to blow up our factories. Hunt them down, one by one if neccessary. "Export" them - preferably permanently.
LOCK DOWN the damned borders. We can put a man on the moon, split the atom, and create cloned sheep for cryin' out loud. We HAVE THE TECHNOLOGY. We just lack the political will to implement it, and claim it is "impossible". I say BUNK. There are those in the 50s and 60s that claimed we couldn't put a man on the moon, either.
IMHO, the border issue is a POLITICAL one that the pols lack the POLITICAL WILL to implement a solution for. Pure and simple, and it will take "2, 3 or 4 big booms" as WestCoastGal says to create a BIGGER political problem that will create an impetus to fix it.