Legal Question in Constitutional Law in South Carolina

Re: Illegal search and seizure

What sort of "ID checkpoint" was this? Police officers can't just pull random drivers over on the road and do what you described, but if you were driving into a restricted area (prison grounds or a military base, for example) then your arrival implies permission for a reasonable search. There are other situations where consent is implied, such as when drivers enter the U.S. from Canada or Mexico and are subjected to a search by the Border Patrol.

Also, police sometimes set up roadblocks when searching for a dangerous criminal suspect or an escaped prisoner, or just to check for people who are driving under the influence. (This is not what I would call an "ID checkpoint", but it could be what you have in mind.) If officers at such a roadblock see evidence of a crime in the car, then they have probable cause to conduct a warrantless search. The extent of the search depends upon a number of circumstances, including the seriousness of the crime they believe is being committed. A "pat-down" search of the driver and passengers is often proper so that the officers can find any concealed weapon before it is used against them, and if the pat-down turns up other contraband then that may be deemed a legitimate seizure depending upon the circumstances.

Drivers normally don't encounter "ID checkpoints", so it seems there is something unusual about your situation and you need to provide a better explanation of what happened. I would need to know more about the circumstances of this search before I could evaluate your rights.