The goal of American warplanes, should they return after three years to the skies over Iraq they patrolled for the previous 20, will be to help “break the momentum" of the Islamic extremist army that threatens the viability of the Iraqi government, according to Pentagon officials.

The White House is reviewing “options” to aid Iraq against the advance of the Islamic State of Iraq and the Levant (Isis), which would stop short of sending US ground troops back to the country where nearly 4,500 of them died between 2003 and 2011.

Several officials said that a potential strike package included targets in Syria as well as Iraq, reflecting Isis' effective erasure of the border between the two countries, and would likely focus on manned warplanes, which are more capable of dynamic targeting against a mobile adversary than are Obama's signature drone attacks.

The White House is adamant that any military campaign should not be a long slog. But time is not on the side of a limited war, with Isis more exposed to attack as it travels in columns down Iraqi roads than it is or will be in cities.

"In the open, they're vulnerable, but as soon as they get into an urban environment, the last thing we need is US fixed-wing [aircraft] trying to help Iraqi security forces trying to fight Isis in an urban combat scenario," said Christopher Harmer of the Institute for the Study of War.

Obama made it clear on Friday that any such strike would be dependent upon a viable Iraqi government plan for sustainable, nonsectarian security. But the president has said little about what he wants to accomplish, and the Pentagon added little.

After four days of fighting, the Islamic State of Iraq and the Levant have seized Iraq's second biggest city, Mosul, and Tikrit, home town of former dictator Saddam Hussein. Guardian

"There is a near-term objective here to try to help Iraq break this momentum," said Rear Admiral John Kirby, the Pentagon press secretary, briefing reporters. He used variations on that formation at least four times to describe the likely mission, but declined repeated requests to define the term. The closest he came was to note that Isis was "clearly interested in geographic gains”.



Kirby's formulation should sound familiar. In 2009, unveiling his Afghanistan troop surge, Obama said: "We will pursue a military strategy that will break the Taliban's momentum.”



The phrase is a masterpiece of messaging. Everyone who hears it thinks they know what it means. But as a declaration of a military objective, it is slippery and noncommittal. It stops well short of declaring to destroy an enemy, take territory away from him or other tangible goals.

But as the Afghanistan war showed, it has an overriding advantage: no one can ever say it has not been achieved. "The tide has turned," Obama said in May 2012, announcing the end of the surge. "We broke the Taliban’s momentum."

On his own terms, Obama wasn't exactly wrong. The Taliban holds less territory than it did in 2009. Yet its insurgency persists, and may well expand after the US leaves Afghanistan in 2016 – much as Isis became the force it now is after the US left Iraq in 2011, the Syrian civil war raged unabated and Iraq's governance descended into sectarian authoritarianism.

President Barack Obama ruled out sending combat troops back into Iraq to quell the rise of Isis. Guardian

Yet the fixation on Isis' "momentum" reflects the reticence Obama feels about getting dragged back into the Iraqi morass. Early in the week, when Isis overran Mosul, Iraq's second-largest city, White House spokesman Josh Earnest lectured the Iraqis to "step up". By Friday, after entire divisions of the US-built Iraqi army had run from the fight, Obama said that whatever military assistance he authorizes will be contingent on Iraqi leaders' "willingness to make hard decisions and compromises on behalf of the Iraqi people in order to bring the country together."

Obama sounded more like a man preparing himself to buy a used car than a commander preparing to order pilots into danger. The reluctance stems from the obvious perils of reengaging in the Iraq war, but his congressional critics seized on it.

"I will not support a one-shot strike that looks good for the cameras but has no enduring effect," said Representative Buck McKeon, the California Republican who chairs the House armed services committee.

Obama will decide within days if the US will, however reluctantly or temporarily, resume one of its most bitter wars. It seems a long time ago that Obama said, on 27 May: "It’s time to turn the page on more than a decade in which so much of our foreign policy was focused on the wars in Afghanistan and Iraq."

But Isis has helped break Obama's momentum.