A ‘what went wrong?’ documentary bristling with answers, “...So Goes the Nation” is a clear-eyed and utterly ruthless dissection of the battle for Ohio in the months leading up to the 2004 presidential election. Zeroing in on the strategic decisions of both major parties, the directors, James D. Stern and Adam Del Deo, illuminate not only the putative blunders of the Kerry-Edwards campaign but also the larger difficulties of the Democratic Party itself. It’s not pretty, but it is instructive.