[Rick Lee]

It's a state matter. Some states have "stop and identify" laws, but the feds don't have that power. IIRC, there was a court case that ruled it was a 5th Amendment issue, since ID'ing yourself to a LEO could constitute self-incrimination if you were wanted by police. I know AZ has a "stop and identify" law. Since I'm almost always in/on a vehicle and/or armed when in public, I can't tell the cop to pound sand just about anywhere. However, you can immediately ask if you're being detained or free to go and that starts the clock ticking for them to come up with a good reason for keeping you longer than 20-30 min.