Border Patrol agent had sufficient articulable grounds for suspicion to stop the vehicle, as it was an unusual vehicle for the road, midnight, a known rendezvous point for migrants, and, in the course of the surveillance, more passengers appeared in the car.
http://www.ca5.uscourts.gov/opinions/pub/17/17-51037-CR0.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.