You seem to misunderstand how things work. I don't have to demonstrate ANYTHING unless and until there is either reasonable (articulable) suspicion that I'm involved in committing a crime or, in some cases, a witness to one. A LEO that wants my ID or detention for investigation has to get to the point of REASONABLE suspicion first, not use contact with me to develop such.
Wouldn't this fall under the 4A?
I find it hard to believe that a cop can stop you for no reason.