Some senior State Department officials argued that the front-line American spotters and attack helicopters would provide critical help to Iraq’s Prime Minister Haider al-Abadi, whom the administration strongly backs. Without some quick battlefield victories, these officials argued, Abadi would be under heavy pressure to rely more on Shiite Iran, which has cast itself as Iraq’s only effective partner in a largely sectarian war with the Sunni-dominated Islamic State.

But the president’s top military commanders argued against a change in strategy that would reduce the onus on Iraqi forces and pull U.S. troops deeper into the war. Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, like other military officials doubted that the gains from using embedded advisers and attack helicopters were worth the possible cost in American blood, said several U.S. officials familiar with his position…

The State Department has “a more optimistic view of the opportunities there than the military does,” a U.S. official said.

A senior Pentagon official described the military’s objections to the higher-risk options in starker terms: “We have become very sensitized to the idea that we don’t want to risk lives and limbs if there isn’t a high probability of a payoff,” said the official. “Our calculus is different.”