The (federal) Posse Comitatus Act does not forbid National Guard elements from engaging in domestic law enforcement activities within their "home" states - rather, it applies to the use of federal armed forces in domestic law enforcement. (It may also deal with the relationship between the federal government and the various state National Guards - or maybe that's something else ... I don't recall at the moment.)
But whether and to what extent the National Guard may be used for such purposes within a given state is up to that state. Perhaps Idaho has some state-level version of Posse Comitatus that is being amended here? As bad as this BS is, I don't see what it has to do with (federal) Posse Comitatus.