Daniel Lubetzky

I say “unthinkable” because, discouraged as everyone has become, most commentary stops short of imagining what an Islamic State victory in the Middle East would look like. The common conviction is that the group is so evil it simply must be defeated — it will just take time.

But let’s test that proposition and think for a minute about what it would take for the group to win. What would success look like for the Islamic State? Essentially, it would amount to the group holding, for the foreseeable future, the core of what it has conquered — roughly half of Iraq and Syria — and exercising a rudimentary sort of governance there, in what it calls its “caliphate.”

What is the foreseeable future? The group is almost certain to survive the Obama presidency. If two years into the next presidency, the Islamic State is still fitfully governing that area, it would be hard, in my view, to not call that a win.

What would have to happen for this to become an almost inevitable outcome? At least four things, none of which lies in the realm of fantasy.

● First, the Islamic State’s opponents would have to fail to marshal a sufficient ground force to take it on. Bombing alone will not be enough. As of now, the Iraqi army is not up to the task, and there is understandably little support in the United States for sending the requisite number of troops, probably somewhere between 10,000 and 20,000. The Arab states have talked about creating a force but have no serious experience with such a project and too little unity to carry it out.

To be sure, we have not given up on training Iraqi soldiers and have also begun schooling 5,000 or so fighters to stand against the Islamic State in Syria. But one thing I took from Vietnam and the conflicts of the past dozen years is that there is a huge difference between training a force and getting it to fight. Good training is necessary but not sufficient.

People don’t fight because they’ve been trained; they fight because they believe in something. At present, the biggest believers in the region are with the Islamic State.

● Second, the Islamic State would have to get into Baghdad. Its dominance of Anbar province puts this step, which would take it a long way toward consolidating its position, within reach.

Many argue that the Sunni-dominated Islamic State cannot “take” Baghdad, a predominantly Shiite city that would be fiercely defended by Shiite militias. But it doesn’t have to take the city to demoralize its opponents, just as the Viet Cong did not need to take Saigon during the 1968 Tet Offensive. It and the North Vietnamese were soundly defeated militarily but still managed to break the south’s fighting spirit and convince many in the United States that the war was unwinnable. The Islamic State only has to show it can breach the city’s defenses by filtering in fighters and weapons and causing chaos.

● Third, Iraq would have to continue to unravel. This would leave the Islamic State’s opponents with a less secure fighting base and the country’s Sunnis, Shiites and Kurds even more adrift. The minority Sunnis remain irreconcilably distrustful of the Shiite-dominated government of Haider al-Abadi. The Kurds’ independence drive appears to be on hold, but if they become the chief fighting force against the Islamic State — the default option if Iraq’s army keeps foundering — their incentive to leave will grow.

● Fourth, Iran would have to shrink from taking on a larger responsibility for defeating the Islamic State. Iranian-trained militias are now assisting Iraqi forces but not to decisive effect. If no other force appears, Iran might be tempted to play the cavalry, throwing in larger numbers of its own soldiers and Hezbollah militia members. But no one wants this, least of all Saudi Arabia, which would then have Iranian forces smack up against its border. And the United States could never acquiesce to this level of Iranian involvement without gutting its regional allies’ faith in its leadership.

These are the harsh realities. The bad options available are such as to induce policy paralysis here and in the Middle East. But the one clear lesson from the past several years is that making no decision is still a decision — and one that can yield even-worse choices.

It seems unavoidable that if the above four conditions come about, the Islamic State will have won, plain and simple, and from that point the challenges will get no easier. The demands of governing might force some compromises on the Islamic State, but — as terrorist states always do — it would eventually look toward external targets such as the United States while posing a continuous threat to its neighbors and clinging to some form of harsh sharia law.

Among the things that could head this off, two are essential. First, we must render hollow the Islamic State’s claim to a “caliphate” by taking back substantial territory. Second, a way must be found to achieve what has so far proved most elusive: an end to the alienation of Sunni populations in Iraq and Syria, the most powerful engine of attraction for Islamic State recruits. This latter goal would require a combination of military pressure, suasion and diplomacy of heroic scale.

But the truth is that nothing else will work.