Legal Question in Constitutional Law in California

Border Patrol can operate a station in Nebraska. Where the Border Patrol operates is not a constitutional issue. As for the stops, they permitted because they are not an "unreasonable" search and seizure. They are a less intrusive stop than the "Terry Stop," so named for the U.S. Supreme Court case that upheld a "stop and frisk" without probable cause to believe a crime had been committed, where the police officer had an objectively reasonable belief that the people he stopped might be armed. Further developments after Terry permit brief stops to "check things out" as long as they are not unduely intrusive interactions with the public. It is the same principal that allows for DUI check-points during the holidays. The basic principal is that a brief non-intrusive stop, with or without ID check, does not constitute an arrest and if it is a "search and seizure," it is not an "unreasonble" one, which is all the Constitution prohibits. Such a brief stop may be used to develop probable cause for a more significant detention or search, which would be a "Terry Stop." In the case of the San Onofre stops, if no probable cause is apparent after a brief conversation, they cannot hold you or investigate further. If they find probable cause for a Terry Stop, they can then and only then move you to the secondary interrogation/search area. If you want to get deeper into this issue, look up Terry v. Ohio, 392 U.S. 1 (1968).