WASHINGTON -- Come September, America might slip closer toward a Weimar moment. It would be milder than the original but significantly disagreeable.

After the First World War, politics in Germany's new Weimar Republic were poisoned by the belief that the army had been poised for victory in 1918 and that one more surge could have turned the tide. Many Germans bitterly concluded that the political class, having lost its nerve and will to win, capitulated. The fact that fanciful analysis fed this rancor did not diminish its power.

The Weimar Republic was fragile; America's domestic tranquility is not. Still, remember the bitterness stirred by the accusatory question "Who lost China?" and corrosive suspicions that the fruits of victory in Europe had been squandered by Americans of bad character or bad motives at Yalta.

So, consider this: When Gen. David Petraeus delivers his September report on the war, his Washington audience will include two militant factions. Perhaps nothing he can responsibly say will sway either, so September will reinforce animosities.

One faction -- essentially, congressional Democrats -- is heavily invested in the belief, fervently held by the party's base of donors and activists, that prolonging U.S. involvement can have no benefit commensurate with the costs. The war, this faction says, is lost because even its repeatedly and radically revised objective -- a stable society under a tolerable regime -- is beyond America's military capacity and nation-building competence, and is politically impossible given the limits of American patience.

The other faction, equal in anger and certitude, argues, not for the first time (remember the transfer of sovereignty to Iraq, Iraqi voters' purple fingers, the Iraqi constitution, the killing of Saddam's sons, the capture of Saddam, the killing of Zarqawi, etc.), that the tide has turned. How febrile is this faction? Recently it became euphoric because of a New York Times column by two Brookings Institution scholars, who reported:

"We are finally getting somewhere" ("at least in military terms"), the troops' "morale is high," "civilian fatality rates are down roughly a third since the surge began" and there is "the potential to produce not necessarily 'victory'" but "sustainable stability."

But the scholars also said: Continued...