That’s not quite true. My understanding is that some things are relaxed for some purposes, but it’s not just a carte blanche. So within 100 miles of the border,

That’s not quite true. My understanding is that some things are relaxed for some purposes, but it’s not just a carte blanche. So within 100 miles of the border, they can operate checkpoints and can stop vehicles for questioning, for purposes of enforcing customs and immigration law. But they cannot just search your car without a warrant (something I believe they can do at the border). It’s really a lot more reasonable than some people make it sound, considering the challenges of policing two massive land borders and a giant coastline, and that their powers are quite limited nonetheless.