What are my rights at a "checkpoint"?

Recently pulled up to a local-police "checkpoint" - check your license and registration, you look all right, go ahead. (This is in the US). Something about this process raised my civics-class hackles. What are the rights of a driver (and the rights of the police) in this case? Do the local... show more Recently pulled up to a local-police "checkpoint" - check your license and registration, you look all right, go ahead. (This is in the US).

Something about this process raised my civics-class hackles. What are the rights of a driver (and the rights of the police) in this case? Do the local authorities have inherent right to see documentation without probable cause to suspect anything is amiss? What happens if one declines?

Pointers to actual case law or documented articles a bonus.
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