Mattis expected to send 800 more troops to southern border

[scipan]

17. it prevents military from directly enforcing domestic laws

such as policing, and so it would prevent them from shooting or detaining people, even brown people south of the border (no authority to enforce laws).

Sources:
https://en.wikipedia.org/wiki/Posse_comitatus
https://abovethelaw.com/2018/10/its-not-a-violation-of-posse-comitatus-if-we-are-preparing-for-war-with-mexico-i-guess/