[jfoutz]

I think you're looking for the phrase `probable cause`. If the officer has probable cause to think you crossed the border, they can search you. I'm not a lawyer, but i think they can search you anyway. It just won't be admissible in court.

edit

to clarify, US law pushes police right up to the edge. there is a preference for false positives rather than false negatives. it's more important to catch all of the criminals than it is to inconvenience some innocent people. The risk of letting one criminal go is much more than cost of detaining a doctor for a couple of hours.

Now, we're in this weird time where that doctor can have 20 years of hippa protected medical records in their pocket that they might be forced to disclose. Historically, that doctor may have some records in a briefcase, but not tens of thousands.