The conundrum President Barack Obama faced when he reluctantly came to the conclusion that the United States would not be able to avoid confronting the threat posed by the Islamic State in Iraq and Syria was how to combat this fundamentalist militia without committing American troops to the fight.

The Iraqi Security Forces melted away in the face of the advance by ragtag ISIS fighters and the Kurdish Peshmerga, while effective, have a limited geographic range of operations. The only reliable militants in the region, then, are the Shiite factions in Iraq. Despite the fact that these groups remain loyal first to Tehran before Baghdad, the United States embraced an alliance of necessity with these groups and sanctioned their role in pushing ISIS back.

Not everyone was perfectly comfortable with allowing Shiite militias to not only serve as the primary force combatting a Sunni militia movement but also to occupy the Sunni towns and cities that it liberated from ISIS control. But some of this strategy’s critics feared that these forces might spark the kind of apocalyptic, region-wide sectarian conflict that ISIS wanted and American military planners long feared. The critics were right.

“U.S.-trained and armed Iraqi military units, the key to the American strategy against ISIS, are under investigation for committing some of the same atrocities as the terror group, American and Iraqi officials told ABC News,” a bombshell ABC report read. “Some Iraqi units have already been cut off from U.S. assistance over “credible” human rights violations, according to a senior military official on the Pentagon’s Joint Staff.”

The investigation, being conducted by the Iraqi government, was launched after officials were confronted with numerous allegations of “war crimes,” based in part on dozens of ghastly videos and still photos that appear to show uniformed soldiers from some of Iraq’s most elite units and militia members massacring civilians, torturing and executing prisoners, and displaying severed heads.

The videos and photos are part of a trove of disturbing images that ABC News discovered has been circulating within the dark corners of Iraqi social media since last summer. In some U.S. military and Iraqi circles, the Iraqi units and militias under scrutiny are referred to as the “dirty brigades.”

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Democratic Vermont Sen. Patrick Leahy told ABC News that this development was particularly disturbing because the United States and the West will ultimately be blamed for the abuses committed by Shiite militias and ISF forces loyal to a Shia-friendly government in Baghdad. He’s right, but Leahy’s solution to this vexing problem is to recommend the U.S. begin “withholding money.” In other words, register America’s disapproval, but not much else.

And while the United States fails to comprehensively confront this ticking time bomb, sectarian tensions in Iraq continue to bubble up to the surface. Returning to Graeme Wood’s seminal essay on ISIS in The Atlantic, the limits of Shia forces’ ability to neutralize the ISIS threat were always apparent to American policy. What’s more, it’s not clear ISIS would not welcome exactly the kind of retributive violence Iraq is witness to today.

Given everything we know about the Islamic State, continuing to slowly bleed it, through air strikes and proxy warfare, appears the best of bad military options. Neither the Kurds nor the Shia will ever subdue and control the whole Sunni heartland of Syria and Iraq—they are hated there, and have no appetite for such an adventure anyway. But they can keep the Islamic State from fulfilling its duty to expand. And with every month that it fails to expand, it resembles less the conquering state of the Prophet Muhammad than yet another Middle Eastern government failing to bring prosperity to its people.

The humanitarian cost of the Islamic State’s existence is high. But its threat to the United States is smaller than its all too frequent conflation with al-Qaeda would suggest. Al-Qaeda’s core is rare among jihadist groups for its focus on the “far enemy” (the West); most jihadist groups’ main concerns lie closer to home. That’s especially true of the Islamic State, precisely because of its ideology. It sees enemies everywhere around it, and while its leadership wishes ill on the United States, the application of Sharia in the caliphate and the expansion to contiguous lands are paramount. Baghdadi has said as much directly: in November he told his Saudi agents to “deal with the rafida [Shia] first … then al-Sulul [Sunni supporters of the Saudi monarchy] … before the crusaders and their bases.”

All the while, the White House dithers and hopes that the music doesn’t stop playing while Obama occupies the chair behind the Resolute Desk.