ISTANBUL — What are the strengths of the Islamic State? I posed this question to two deeply knowledgeable observers — a European diplomat and an American former official — and the picture they painted is worrying, though not hopeless. Defeating the group would require a large and sustained strategic effort from the Obama administration — but could be done without American ground troops in any significant numbers.

The European diplomat, stationed in the Middle East, travels in and out of Syria and has access to regime and opposition forces. He agrees with the consensus that the Islamic State has gained considerable economic and military strength in recent months. He estimates that it is making $1 million a day in Syria and Iraq (each) by selling oil and gas (though American experts believe this number is too high in Iraq).

The Islamic State’s military strategy is brutal but also smart. The group’s annual reports — it has issued them since 2012 — detail its military methods and successes to impress its funders and backers. The videos posted online of executions are barbaric but also strategic. They are designed to sow terror in the minds of opponents, who, when facing IS fighters on the battlefield, now reportedly flee rather than fight.

But the most dangerous aspect of the Islamic State, this diplomat believes, is its ideological appeal. It has recruited marginalized, disaffected Sunni youth in both Syria and Iraq who believe that they are being ruled by apostate regimes. This appeal to Sunni pride has worked largely because of the sectarian policies of the Baghdad and Damascus governments. But IS has also worked because of the larger collapse of moderate, secular and even Islamist institutions and groups — such as the Muslim Brotherhood — throughout the Middle East.

How to handle this challenge? The American, a former senior administration figure, counsels against pessimism. “IS is not nearly as strong as al-Qaeda in Iraq was in its heyday,” he notes, downplaying recent reports that the militant forces contain within them fearsome elements of Saddam Hussein’s disbanded army. “We fought that army. It was not very impressive,” he notes. IS could be defeated, he says, but it would take a comprehensive and sustained strategy, much like the one that undergirded the surge in Iraq.

“The first task is political,” he said, supporting the administration’s efforts to press the Iraqi government to become more inclusive. “We have more leverage now than at any time in recent years, and the administration is using it.” If this continues, the next step will be to create the most powerful and effective ground force that can take on IS — which would not be the Free Syrian Army but rather a reconstituted Iraqi army. Built, trained and equipped by the United States, “it’s actually got some very effective units. Iraqi special forces were trained in Jordan and are extremely impressive,” he said, pointing out that it was those forces that recaptured the Mosul Dam recently. It has underperformed because then-Prime Minister Nouri al-Maliki transformed it in the last three years into a sectarian and loyalist force.

The reconstitution of Iraqi army units will require the firing of the Shiite commanders that Maliki appointed. This again mirrors the surge, during which 70 percent of Iraq’s battalion commanders were replaced to create a more inclusive and effective fighting force.

Once the Iraqi army is effective and fighting, the former American senior official said, it should employ the “oil spots” strategy of the surge, clearing and holding areas. But the key to that would be winning the trust of the local Sunni populations. That same approach could be used in Syria, with the Free Syrian Army using money and security to win over locals who oppose Assad but now ally with IS out of fear rather than conviction.

The two observers agreed on one central danger. The temptation to gain immediate military victories over IS could mean that the U.S. would end up tacitly partnering with the Assad regime in Syria. This would produce a short-term military gain but a long-term political disaster. “It would feed the idea that the Sunnis are embattled, that a Crusader Christian-Shiite alliance is persecuting them and that all Sunnis must resist this alien invasion,” the European diplomat said. “The key is that Sunnis must be in the lead against IS. They must be in front of the battlefield.”

The strategy that could work against the Islamic State is nothing less than a second Sunni Awakening. It’s a huge challenge but appears to be the only option with a plausible chance of success.

Fareed Zakaria is a syndicated columnist. His email address is: comments@fareedzakaria.com.

Copy the Story Link