Earlier quoted context omitted.
Is simply crossing a border a "reasonable" search and seizure under the Fourth Amendment? Is there a legal precedent for that?
https://en.wikipedia.org/wiki/Border_search_exception Since the first border search statute was enacted in 1789, customs officials have essentially been authorised to search anything crossing the border, without warrant. It was approved by the first US congress, which counted James Madison, Alexander Hamilton, George Washington and John Adams among its members. The original target was ships that might be carrying tax…
That's not an argument for warrantless searches, though. A thing that's regulated is obviously older than the regulation. Killings are older than “thou shalt not kill.”