I didn't know this, but pay attention.

"[T]he Department of Homeland Security has claimed the authority to interrogate and search people anywhere within 100 miles of a US border, even without suspicion of wrongdoing or warrants." [Video montage reveals resistance to DHS checkpoints in the southwest].

The ACLU map shows the constitution-free-zone where one can be  interrogated on public streets and trains, and have their electronics confiscated at airports.