If we accept the 90+% failure rate in the 2016 real-world test of TSA sceeners to be representative of the proficiency of the TSA as a whole, then we should also accept that the real role of the TSA is to reassure the traveling public.  Put another, more cynical way, it's just a visible method our government is using to show it's doing something (but not that it actually does anything that justifies the salaries paid or the millions of dollars paid to U.S. companies for the associated hardware, training and maintenance - not to discount the millions of man hours lost waiting in line by the traveling public).

I realize that trying to prove a negative is difficult if not impossible, but just how many 9/11 terrorist attacks do you guess the TSA has prevented since its inception?  Or, if we consider something we CAN measure, just how many would-be terrorists have been caught or prevented from boarding planes by alert TSA screeners?  One?  Two?  Any?