Someone will have to fight Islamic State militants on the ground in Iraq. But it still is unclear who that will be.

Defense Secretary Ash Carter told the House Armed Services Committee on Wednesday that training efforts in Iraq so far have been “slowed” by a lack of Iraqi volunteers, sparking concerns about how effective those security forces can be in pushing back the advancing enemy.

U.S. officials had hoped to train about 24,000 new Iraqi fighters by this fall but so far have seen only a third of that total in the four training sites set up across the country. […]