They are subject to the legal system of the US. It's just that, within 100 miles of any border, Constitutional rights are limited, and non-citizens have fewer rights at border crossings.
CBP won't get away with using that rule to search someone that has not recently crossed the border.
When they setup checkpoints, they can't do arbitrary searches (they can just check vehicles for aliens). So they have less leeway in those situations than when they are doing a border search.
Example from a while back: http://www.ocregister.com/articles/yuma-156221-drug-bratcher...
That's not what I said.
> What are your Constitutional Rights at border crossing? What are rights of non-citizens?
https://mobile.nytimes.com/2017/02/14/business/border-enforc...
https://www.google.co.in/url?q=https://www.acluaz.org/sites/...
you're right to a large extent.
https://www.aclu.org/other/constitution-100-mile-border-zone