What more could the United States do? There are several options, some already under consideration by the administration, officials say.

The United States could send more advisors and trainers to Iraq to expand the relatively small force already there and allow them to work with more Iraqi units, or even accompany Iraqi forces onto the battlefield.

Although the administration has already increased military aid to the Iraqi army, it could be tougher in demanding that Baghdad’s defense ministry implement its promises to arm Sunni forces before more aid arrives.

The U.S. could also consider arming Sunni forces directly. That step, however, could undermine Abadi and accelerate Iraq’s division into sectarian camps.