John McCain has set off a firestorm by suggesting that the timing of the withdrawal of US forces from Iraq is "not too important." What is important, he said, are the casualties in Iraq, pointing to long-term US troop presence in Japan, South Korea, and Germany. He should be commended for his "straight talk" in articulating what he believes, despite its unpopularity.

But Senator McCain has yet to give the American people clear answers to three fundamental questions: What, exactly, are the political objectives of keeping large numbers of American soldiers in Iraq for years to come? What plausible outcome would benefit the United States enough to justify the wrenching costs of achieving those objectives? And what, concretely, is the strategy for getting there?

McCain may genuinely believe there is still a political objective, albeit a far more modest one than President Bush and the war's supporters originally articulated, that can justify the sacrifice of still more American lives and treasure. But if he can't do better than slogans such as "winning" and "stability," it's hard to avoid the conclusion that such an objective simply doesn't exist. And in that case, we can add one more exorbitant cost to the war's bill: the death of strategy.

Carl von Clausewitz famously explained that war is simply a continuation of policy by other means. Distasteful as that might seem, it has the virtue of ruling out wars that have no defined political objective. Writing under the shadow of the political upheavals resulting from the Napoleonic wars, the Prussian strategist understood that war is inherently political, and not merely a technical and mechanical confrontation between armies. As such, "victory" cannot be defined solely by the body count of the enemy.

McCain, who fought in a conflict the US lost despite defeating the Viet Cong and the North Vietnamese Army in every battle of military consequence, should instinctively appreciate Clausewitz's insight.Instead, McCain, Bush and many leading Republicans chide Barack Obama and fellow Democrats for refusing to concede that the US is now "winning" in Iraq. But in their focus on tactical-level progress – military fatalities and sectarian killings are down, and pacified neighborhoods are up – they duck the more fundamental question: What larger strategic and political objectives are being served?

"Stability" is hardly a worthy political objective for the sacrifices US soldiers and taxpayers continue to make in Iraq. From an American perspective, stability matters only if its terms are consistent with the US national interest; stability for its own sake is meaningless.

Just what type of newly "stable" Iraq can emerge under the protection of American forces? There are several possibilities.

The first is that after the "moderate" Sunni Arabs (including Saddam Hussein's former henchmen) wipe out Al Qaeda, and after the Shiite establishment consolidates supremacy on its side of the sectarian divide, there will be an Iraqi civil war. Like other civil wars, it will end, after months, years, or decades, either in compromise, the decimation of one side, or partition.

Another possibility is that the Arab Iraqis will reach some kind of compromise so as to focus their energies on destroying the US-backed Kurdish statelet and blocking Turkish inroads into northern Iraq.

Most likely, the Shiite Arab forces will retain control of most or all of Mesopotamia. Though historical animosities between Arabs and Persians are strong, even among Shiites, such an Iraqi government will probably continue to be penetrated by Iranian agents of influence and tilt toward Tehran.

Which of these plausible outcomes is a worthy political objective that could justify even a reduced level of American deaths, further damage to US global standing, and continued deferral of attention to other pressing challenges?

Some will argue that the simple fact of planting democracy in Iraq – assuming it could be achieved in one of the above scenarios – would suffice as a political objective calling for further American sacrifice.

But with the experience of democratic elections in the Palestinian territories, and even to some extent in Iran, can we reasonably expect that an Iraqi democracy without the presence of American troops would respect individual rights and be friendly to the US?

On the campaign trail this summer, McCain may be right in repeating his hope that the US will win the Iraq war by 2013. The question we should be asking him is this: Win what?

• Robert Dujarric is director of the Institute of Contemporary Japanese Studies at Temple University Japan in Tokyo. Andy Zelleke is a lecturer in public policy at the Harvard Kennedy School and codirector of its Center for Public Leadership.