By expanding his military campaign against the Islamic State group, President Barack Obama hopes to reverse the militants' momentum in Iraq, squeeze their sanctuary in Syria and erode their recruiting appeal across the greater Mideast. Those are key steps toward Obama's stated goal of eventually destroying the extremist group.

The strategy's success, however, also hinges on a set of more difficult moves: effective coordination with Iraqi and Kurdish ground forces, undercutting financial and ideological support for the Islamic State group, and building up anti-Islamic State forces in Syria without strengthening the regime of President Bashar Assad, which Obama considers illegitimate.

These U.S. gains are unlikely to occur quickly, but broadening U.S. airstrikes in Iraq and extending them to Syria could "change the reality and the perception of whether ISIL has the momentum or whether they are being rocked back on their heels," said Michele Flournoy, the Obama administration's first policy chief at the Pentagon and now the chief executive officer at the Center for a New American Security think tank. ISIL is an alternative acronym for the Islamic State group.

Undermining the Islamic State group's popular image as a military steamroller is especially important, particularly in the short run, she said.

"On the Iraq side of the border it has already begun," she said.

Five weeks of U.S. airstrikes against Islamic State forces in northern and western Iraq have taken a military and perhaps psychological toll, compelling those forces to disperse and assume more defensive positions, according to U.S. defense officials. That has stalled their offensive, which swiftly routed Iraqi troops in the north in June and gave Islamic State fighters the appearance of being an unstoppable force, prompting Obama to begin limited bombing Aug. 8.

Last weekend, the U.S. began airstrikes around the Haditha Dam west of Baghdad, marking an expansion of the mission. With his announcement Wednesday, Obama essentially has lifted all restrictions on Islamic State targets in Iraq, meaning the air campaign will intensify, broaden and perhaps exact a heavier toll. To facilitate the additional strikes, Obama authorized U.S. soldiers to begin embedding with the Iraqi army — not to fight alongside them but to help them profit from U.S. airstrikes.

Obama made clear the task won't be easy.

"Now it will take time to eradicate a cancer like ISIL," Obama said in his televised address to the nation. "And any time we take military action, there are risks involved."

The Pentagon said Wednesday, before Obama's speech, that U.S. warplanes had conducted 154 airstrikes in Iraq so far, damaging or destroying 212 Islamic State targets, including 162 vehicles.

Obama has been firm in refusing to commit U.S. ground combat forces in Iraq, having staked his 2008 presidential candidacy on ending the war started by his predecessor. But expanding the air campaign means the U.S. military role will extend beyond the fighters, bombers and armed drones that have carried the bulk of the attack load so far, supported by refueling aircraft. It will include 150 U.S. military advisers operating in the field with Iraqi commanders, plus 125 to fly and maintain Iraq-based U.S. surveillance aircraft to collect targeting information for Iraqi troops.

Anthony Cordesman, a defense analyst at the Center for Strategic and International Studies, a think tank, says only about one-third of the Islamic State force — which others have estimated may total 20,000 to 30,000 fighters — are highly skilled. Cordesman believes Iraqi government forces can handle them with U.S. assistance, although he predicted in an analysis published Tuesday that it probably will take several years to create sufficient political and military unity in Iraq to fully defeat the Islamic State forces there.

"There is no clear timeframe for a similar defeat in Syria," he added.

Flournoy, who served as the undersecretary of defense for policy from 2009-2012, said this week that Obama has little choice but to extend the fight to Syria. She said U.S. planes could target Islamic State headquarters buildings, training sites and supply lines used to reinforce its fighters in Iraq.

"This will take time" to undercut the extremists' ability to function as a land army and an administrator of large chunks of Iraqi territory, she said. "This is not going to happen in a matter of weeks or months."

Douglas A. Ollivant, a retired Army officer who was director for Iraq on the National Security Council in the late stages of the Iraq War, said U.S. airstrikes in Syria would be designed to support the ground war in Iraq and make Syria less useful as a support base for Islamic State forces. But that approach has its limitations.

"We're under no illusions that doing airstrikes alone in Syria is going to kick them out of Syria," he said.

In the longer run, more fundamental shifts could create a "new map of Mesopotamia," according to Bing West, a retired Marine officer and author of "One Million Steps, a Marine Platoon at War."

After a few years of U.S. bombing coordinated by special operations forces on the ground in Iraq, the Islamic extremists will be squeezed out and Sunni tribal leaders in western Iraq are likely to coalesce to form what amounts to an independent state, as the Kurds have done over the past decade in northeastern Iraq, he said in an email exchange Wednesday.

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