[GirlShortstop]

stopping every vehicle in the area for search and or seizure is not unreasonable.
     "In the area" is key imho. How does the following scenario grab you:  police find a gun in the car of one of these vehicles searched (not a white van). It turns out to be the perp/s. American/s, unaffiliated with a terrorist group.  But their case is tossed because the evidence is a result of of improper search and seizure on the part of the police.  Possible?  I'm curious and would like to feel more confident in the LE efforts that I've seen so far.

[Howlin]

Well, your own hypothetical says that the case would be tossed if it was an improper search.