If you wondered why federal troops are barred from civil law enforcement, Charles Lane’s Retropolis column spells it out in detail. And all this bluster from 1600 Pennsylvania Ave. NW, Washington, D.C., about ordering the equivalent of a heavy Army brigade to the border to do what: string concertina wire; muscle to enforce immigration laws? Not their job — by statute [in reality then, to get around enforcing federal voting rights acts and let the states have their way as to who could exercise the franchise]. That was the underlying reason behind the 1878 end-of-Reconstruction act. The federal government shutdown of that time that led to Posse Comitatus started with vetoing the Army spending bill and spread like cancer through the other departments.