Sure, but if you're driving in NM or TX or AZ, what constitutes that reasonable basis for a stop? As long as the car is legal, there can't be any, yet they still do roving patrols. The also stop buses and trains mid-transit (not at stations), which again, hard to conceive of why that would be necessary - if they know an illegal is on a bus/train, sure stop it and get the person, but asking everybody onboard - should be illegal.