WASHINGTON -- Before Gen. David Petraeus' report, and to give it a context of optimism, the president visited Iraq's Anbar province to underscore the success of the surge in making some hitherto anarchic areas less so. More significant, however, was the fact that the president did not visit Baghdad. This underscored the fact that the surge has failed, as measured by the president's and Petraeus' standards of success.

Those who today stridently insist that the surge has succeeded also say they are especially supportive of the president, Petraeus and the military generally. But at the beginning of the surge, both Petraeus and the president defined success in a way that took the achievement of success out of America's hands.

The purpose of the surge, they said, is to buy time -- "breathing space," the president says -- for Iraqi political reconciliation. Because progress toward that has been negligible, there is no satisfactory answer to this question: What is the U.S. military mission in Iraq?

Many of those who insist that the surge is a harbinger of U.S. victory in Iraq are making the same mistake they made in 1991 when they urged an advance on Baghdad, and in 2003 when they underestimated the challenge of building democracy there. The mistake is exaggerating the relevance of U.S. military power to achieve political progress in a society riven by ethnic and sectarian hatreds. America's military leaders, who are professional realists, do not make this mistake.

The progress that Petraeus reports in improving security in portions of Iraq is real. It might, however, have two sinister aspects.

First, measuring sectarian violence is problematic: The Washington Post reports that a body with a bullet hole in the front of the skull is considered a victim of criminality; a hole in the back of the skull is evidence of sectarian violence. But even if violence is declining, that might be partly because violent sectarian cleansing has separated Sunni and Shiite communities. This homogenization of hostile factions -- trained and armed by U.S. forces -- may bear poisonous fruit in a full-blown civil war.

Second, brutalities by al-Qaeda in Iraq have indeed provoked some Sunni leaders to collaborate with U.S. forces. But these alliances of convenience might be inconvenient when Shiites again become the Sunnis' principal enemy.

Congressional Democrats should accept Petraeus' report as a reason to declare a victory, one that might make this fact somewhat palatable: Substantial numbers of U.S. forces will be in Iraq when the next president is inaugurated. The Democrats' "victory" -- a chimera but a useful one -- is that Petraeus indicates there soon can be a small reduction of U.S. forces.

To declare this a substantial victory won by them requires Democrats to do two things. They must make a mountain out of a molehill (Petraeus suggests withdrawal of only a few thousand troops). And they must spuriously claim credit for the mountain. Actually, senior military officers have been saying that a large drawdown is inevitable, given the toll taken on the forces by the tempo of operations for more than four years.

But Democrats cannot advertise a small withdrawal as a victory without further infuriating their party's base, the source of energy and money. The base is incandescent because there are more troops in Iraq today than there were on Election Day 2006, when Democratic activists and donors thought, not without reason, that congressional Democrats acquired the power to end U.S. involvement in Iraq.

A democracy, wrote the diplomat and scholar George Kennan, "fights for the very reason that it was forced to go to war. It fights to punish the power that was rash enough and hostile enough to provoke it -- to teach that power a lesson it will not forget, to prevent the thing from happening again. Such a war must be carried to the bitter end." Which is why "unconditional surrender" was a natural U.S. goal in World War II, and why Americans were so uncomfortable with three "wars of choice" since then -- in Korea, Vietnam and Iraq.

What "forced" America to go to war in 2003 -- the "gathering danger" of weapons of mass destruction -- was fictitious. That is one reason why this war will not be fought, at least not by Americans, to the bitter end. The end of the war will, however, be bitter for Americans, partly because the president's decision to visit Iraq without visiting its capital confirmed the flimsiness of the fallback rationale for the war -- the creation of a unified, pluralist Iraq.

After more than four years of war, two questions persist: Is there an Iraq? Are there Iraqis?