The native tribes want to take over the horse racing industry?
Pari-mutual wagers are generally associated with horse racing (and dog tracks I suppose) but there maybe others as well when there are multiple entrants in a contest. The money bet on a race is put into a pool, from which the odds are calculated based on how much is placed on each contestant, with the house taking something like 17% off the top and then paying out to winning tickets according to those odds.
The device-this was decided long ago when they outlawed offshore bookies that were state licensed and acting lawfully in Antigua Jamaica, UK, Australia, Costa Rica etc......
Nationally now, the lawful online sports books geo fence within their licensed state=the device again.