There's a big problem with President Obama's new war against the Islamic State in Iraq and Syria (ISIS): it can't be defeated by military means alone. And the more Obama escalates, the more he runs the risk of forgetting that once-central element of his policy— with disastrous consequences.

Obama's new strategy in Iraq and Syria, announced in a Wednesday evening address, rests on the theory that the Iraqi army, Syrian rebels, and the US Air Force can defeat ISIS on the battlefield. That might be true — if all of the political stars align properly. But by declaring an open-ended, years-long war against ISIS, Obama risks trying to solve a fundamentally political problem by military means.

To understand this problem, consider everything that has to go right for Obama's strategy to work out. Success, as Obama defines it, means that Iraqi and Syrian forces have taken away ISIS's "safe havens" — or its control over territory. That means getting the local Sunni populations, who have thrown tacit support to ISIS, on board with pro-American Syrian rebels and the Iraqi government.

Even assuming the Iraqi and Syrian rebel forces can be made strong enough to take on ISIS in purely military terms, there's a list of everything that needs go right — politically — for Obama's strategy to work out:

The Iraqi government needs to stop repressing and systematically disenfranchising Sunnis. It also needs to accommodate their demands for positions of power in government in perpetuity, so ISIS doesn't just pop back up after the US leaves. The US must avoid sending the signal that it's coordinating with Iran, which would put it on the Shia side of a sectarian war. Syrian rebels armed and trained by the US don't simply take their new weapons and defect to ISIS or Jabhat al-Nusra, the local al-Qaeda affiliate. US airstrikes and US allied military campaigns need to avoid killing large numbers of civilians, which could cause a pro-ISIS popular backlash. If the US actually does manage to demolish ISIS's control on territory, it needs to ensure that neither Syrian President Bashar al-Assad nor al-Qaeda simply take over the land that ISIS has vacated. The United States has to do all of this without deploying ground troops or otherwise getting caught in a bloody, brutal quagmire.

For the outcome to end well, every single one of these events must go the right way. There's a reason that one US General told the Washington Post that the new campaign in Syria is "harder than anything we've tried to do thus far in Iraq or Afghanistan." Given how those wars ended up, that's a pretty ominous comparison.

That's not to say that Obama's plan is doomed to failure. Long odds aren't the same as guaranteed disaster. Rather, it's to point out that for Obama's plan to work, he needs to address the fundamentally political roots of the conflict: the sense, among Iraqi and Syrian Sunnis, that ISIS is their best option as compared to the repressive Iraqi government and unremittingly brutal Assad regime.

The US can't credibly threaten to stop its assistance to Baghdad if the new government takes a brutally sectarian turn

That means, for example, that political reform in Baghdad is much more important in the long run than airstrikes or training for the Iraqi army. Yet Obama appears to be treating the political problem as mostly solved. "I've insisted that additional US action depended upon Iraqis forming an inclusive government, which they have now done in recent days," he said on Wednesday night.

But the new Iraqi government has existed for all of three days. It's still led by the Shia Islamist Dawa party. There is no guarantee that new Iraqi Prime Minister Haider al-Abadi will govern in an inclusive manner.

Yet Obama has now committed the US to a multi-year, indefinite campaign against ISIS. Given that the US has pledged to fight ISIS everywhere until it's destroyed, and its strategy for doing that depends critically on military cooperation with Iraq, it cannot credibly threaten to stop its assistance to Baghdad if the new government takes a brutally sectarian turn or falls apart. In other words, the US may have just committed to getting in bed with a Shia sectarian regime.

And Syria is, of course, even more complicated. The Iraqi government, for all its faults, is far stronger and more unified than Syria's moderate rebels. Managing the political divisions between the rebels and preventing US-trained soldiers from defecting to ISIS or al-Qaeda is on its own difficult. To do that while simultaneously attempting to peel Syrian Sunnis away from ISIS and pushing ISIS out of its territory without allowing Assad to occupy the land in its absence requires astonishingly precise political and strategic juggling.

The big risk, then, is that all of the political calculations fall to the wayside in the face of stepped-up military efforts. The more the US starts to see ISIS through the prism of a military campaign, the more we focus on arms rather than politics as the answer.

"I think the problem with our narrative about Iraq is that 99.5 percent of the people we had in Iraq were uniform, and therefore we have a very military-centric lens," Doug Ollivant, the National Security Adviser for Iraq from 2005 to 2009, told Vox in June. For Obama's ISIS strategy works, he needs to get a new set of lenses.