I suspect that one of the original ideas behind the National Guard was to provide some sort of civil powers assistance force, but there has always been a great deal of resistance in this country to using military forces for such functions. Just look at (for one example) the debate surrounding Sheridan's use of the military in the aftermath of the Chicago Fire.

Still...this might be an interesting NG function, or something that might better lie in their sphere of influence as opposed to the Regulars.