I wouldn't be surprised to see these deployed in the international arrivals area at some time in the future.

Subject every pax entering the US, citizen or not, to a drug sniff.

I'm not sure how that would work, particularly if you were returning from AMS and had visited a coffee shop. (For that matter, can a US citizen be prosecuted in the US for having visited an AMS coffee shop? For having indulged at that coffee shop?)

At the very least, even if the pax could clear him/herself after an invasive and protracted secondary, he/she would probably be on a CBP watch list and face a secondary for the rest of his/her life.