Originally Posted by XGSC

My guess is two fold, and it depends on how the checkpoint is set up. The ID checkers are verifying ID and a document which permits entry to the sterile area, IE boarding pass, Gate pass, Airport ID. They MAY also be sending selectees to the additional screening lane. The Magnitometer person is double checking whether you need to be selectee screened. If they miss a selectee, the airline must refuse boarding until that pasenger is screened. Causes a lot of trouble for the carrier and the TSA. So they double check, seems to be the lesser of two weevils,