I encounter this frequently at IAD. There are 1-2 more TSOs standing within 5-10 feet of the TDC stations, and they stop about 1 in 3 pax to ask to see their BP and ID.

Rarely, they do an ETD swab of one's hands (I've run into that only once, but the 2nd ID check probably 6-8 times this fall).

Honestly, is there ANY (valid) reason for an ID & BP check within a couple of paces of the original document check? On at least one occasion, this TSO had clearly seen two different TDCs look at my BP & ID already (they were conferring over whether or not NEXUS was acceptable), yet felt the need to take a look herself, too.