Borderless Vigilantism: The Nativist US Militias Entering Mexico
bellingcat.com
bellingcat.com
Crossing the border armed in camo suits is definitely illegal in both countries.
Ironically, the second amendment also requires that militias be "well regulated," but because we have to use the original 18th century meaning of terms, that doesn't mean regulated by the state, but simply armed and ready, so essentially just self-regulated.