Well to get around the Posse Comitatus Act, just turn the police into quazi military organizations. Tie enough of their funding to federal grants and they become more beholden to the feds than there local governments.
So yes it does sound wonderful to fully equip the local police like this... But a government strong enough to right all wrongs is a government strong enough to enact laws contrary to the will of the governed and to break the contract between the governing and the governed by force.
You honestly think one of those things wouldn’t come in handy in El Paso/Cd. Juarez? That Sheriff, a supporter of whom I am not, is nevertheless on the front lines of the border wars. A government that is unable to protect its borders is no government at all.