[dware]

Sovereign Nation means Sovereign Nation.

[Sacajaweau]

A little tricky but not quite as clean as you think since Indians are citizens, too and are subject to our laws.

It's complicated.

[WMarshal]

If the tribe won’t police the border with Mexico then cut off all federal aid to the tribe and start enforcing the tribe’s borders like you would Mexico.

[DesertRhino]

“Sovereign Nation means Sovereign Nation.”

Kinda. And kinda not. The FBI and US Marshall service goes out there. The department of interior runs a lot of their world. They do not have a military.
They cannot pass laws that violate the US constitution. For example they cannot make free speech illegal. They cannot print their own money.

They are slightly more sovereign than a state.

[Oldexpat]

Good. Put them on the Mexican side of the fence and force them to cross a border to get in the US. Then cut of the money.

[Stingray51]

Complete bs. Send in the Army.