We are three months into our newest war, the one against Daesh (Islamic State of Iraq and the Levant) and nobody is happy with the way it is going.

Hawks complain that US President Barack Obama is not committing enough military force to win. Doves, noting that Obama just doubled the number of US troops in Iraq, worry that the conflict will become the kind of slippery slope that drew the US into quagmires such as Vietnam. And critics on both sides charge that the US administration has no clear strategy for success.

There is an element of truth in all those critiques, but they all miss the point.

What has so many people perplexed, I think, is that in Iraq, Obama has — without announcing it — broken with a principle that has dominated US military thinking for nearly a quarter of a century: The Powell Doctrine. This is a set of war principles laid out by General Colin L. Powell when he was chairman of the Joint Chiefs of Staff in the 1990s. Among other things, Powell felt that the US should no longer fight the kind of “limited war” it had tried to fight in Vietnam. If the US went to war again, he advised, it should use all the military power at its command to win as quickly and decisively as possible.

That was the thinking that guided the first Gulf War in 1991, the US invasion of Iraq in 2003, and even — in different forms — the long counter-insurgency wars in Afghanistan and Iraq that followed: Every element of American military power was thrown into the fight, including tens of thousands of US troops on the ground.

Not so in the fight against Daesh, however, — even though Obama and his aides have described the group as a direct threat to US citizens and US interests. This time, the president has drawn a line to limit what American troops in Iraq will do: They can advise, assist and train Iraqi forces, but they will not participate in ground combat. Last week, asked if there were circumstances under which he would send US troops into ground combat, Obama said: “If we discovered that [Daesh] had got possession of a nuclear weapon, and we had to run an operation to get it out of their hands, then yes.” Otherwise, no.

Even more striking, officials say the US has held back some aid from the Iraqi government, its most important ally in the fight against the militant group, to make sure Prime Minister Haider Abadi delivers on his promises to build a more inclusive regime — specifically one that offers more to Sunni Arabs, whose grievances opened the way to Daesh’s rise.

Army General Martin E. Dempsey, chairman of the Joint Chiefs of Staff, explained the idea at a congressional hearing this month — and said the Powell Doctrine of maximum available force was not suited to a situation like the one posed by Daesh. “I just don’t see it in our interest to take this fight on ourselves with a large military contingent,” Dempsey said. Too much US force, he warned, could “generate antibodies within the population that could actually be counterproductive to what you’re trying to achieve.” Besides, he added, the US has been there before. “This is my third shot at Iraq,” Dempsey said later, noting that he had served in both the earlier wars. This time, he said, instead of “taking ownership” of the war, the US wants to make sure ownership stays with the Iraqis, “and then hold them accountable for the outcomes”.

And that is how Obama hopes to avoid a slippery slope: By drawing a firm limit to US involvement. The limit is not the number of troops in Iraq, which is growing from about 1,600 to about 3,100. It is in the prohibition against ground combat and in the insistence that aid will flow only as long as the Iraqi government pulls its weight, including allowing US training and aid to Sunni tribes that volunteer to fight Daesh.

What are the risks of ignoring the Powell Doctrine and launching this new experiment in limited war?

One is that the conflict will last longer. Obama has warned that the fight against Daesh, which has no more than 18,000 hard-core members, will last a long time. Dempsey has estimated it will take three to four years, about the same amount of time as the US had spent in Second World War. The other risk is that limiting US involvement — even as firm a limit as Obama has imposed so far — is no guarantee against future pressure to take another step down the slippery slope.

In wars, unexpected things happen, and planning has to be nimble. As Dempsey acknowledged acerbically last week: “Yes, we have a strategy ... But here’s what I’ll tell you about that strategy: It’s going to change. It’s going to change often.” And if the conflict drags on long enough, America will have a new president in office, facing the same pressure to do more. Every politician who is thinking about running for president right now should be praying earnestly that Obama’s Plan A works.

— Los Angeles Times