Oh, wait, I forgot, we are still in the mode of "stop the specific mode of each particular attack".
Blow up building with fertilizer bomb-> must track all sales of fertilizer
Shoe bomber -> must scan all shoes
Underwear bomber -> must scan through underwear
Bomb with black powder -> must start scanning everywhere for black powder
Bribe TSA agents to let drugs through -> oops, no way to check this, just forget about it.
Unfortunately, using this method of "prevention" will take hundreds of years, thousands and thousands of different bombs, and the elimination of most every civil liberty you have to "win the war on terrorism".