[MRM]

There is no US identification card and there is no law that you must carry ID on you. Several European countries used to have national ID cards and you were required to carry your papers with you at all times, a la the USSR where the cops could demand to see your papers, confiscate them, and the next cop takes you in for not being in possession of your ID. There are deep and important Constitutional considerations that have so far prevented a national ID card and requirement to carry ID.

Obviously you have to have a driver's license with you when you drive, but that's just a state law that's part of driver regulation. Usually driving without a license in possession is a petty offense with a payable fine as a penalty as long as you actually do have a license. In Minnesota, I think the law is still on the books but it is not enforced as long as the driver can be identified and does have a valid license.

If you are lawfully stopped by a cop you must identify yourself. You don't have to have an ID on you, but you have to say who you are. If they have proper authority to detain you, they can hold you long enough to verify your identification, run you for warrants, etc. How long they can hold you and what lengths they can go through to ID you depends on the circumstances. If you are arrested you have to identify yourself and can be held until your identification is verified.

As far as I know, it is an open question whether a cop can encounter you in circumstances that do not rise to the level of a "stop" for which probable cause and reasonable suspicion do not exist, and demand identification. If a cop encounters you and is talking to you, generally speaking they can do a "Terry" frisk of you to make sure you don't have any obvious weapons that could threaten the cop. This is the pat down of outer clothes that you see cops do sometimes on TV when they stop a snitch in the street and roust him to get information out of him. Again, whether they can search you and the invasiveness of the search is on a continuum that depends on the circumstances.

I do not believe that it is settled law from the US Constitution that cops who get close enough to a Terry stop and frisk can demand ID without any other attachable suspicion. I don't believe the US Supreme Court has ever decided definitively whether cops can just stop people and demand their IDs. The justification for Terry frisks is officer safety and the search can't go beyond looking for weapons that are immediately accessible. The same justification doesn't hold true for IDs.

I know several states have ruled on this issue under their state constitutions and have generally found that cops can't just walk up to you and demand ID without a reasonable suspicion or probable cause to stop you. My analysis is that cops can't stop you and demand an ID without some other conduct or suspicion justifying the need to identify you, but neither my state's nor the US Supreme Court tend to take my advice on how to rule.