follow the money.
drugs sell for CASH.
CASH is LAUNDERED in CASINOS (and REAL ESTATE, political contributions and Non Profits, etc.).
Who runs the border casinos? Reservation politricksters.
As of 2011, there were 460 gambling operations run by 240 tribes, with a total annual revenue of $27 billion.
https://en.wikipedia.org/wiki/Native_American_gaming