If 0.01% of people are nefarious, and they check 99.9% of the time, that’s still 1/10,000,000 chance a nefarious person gets through.
As long as they don’t do this often, doing that once probably has near zero impact on security.
(Please don’t pick apart the assumptions that nefarious people always get found by screening, or that the TSA works, that’s not the point I’m making — just trying to say a one off unpredictable dropping of guard doesn’t hugely benefit nefarious actors)