The urgency behind the Obama administration’s revitalized debate over launching air strikes in Iraq is not solely caused by the impending “humanitarian catastrophe” referenced by White House press secretary Josh Earnest during a briefing on Thursday. Fighters from the Islamic State (Isis) are now threatening Iraqi Kurdistan, long a bastion of security, which would open a new and ominous chapter in the war.



For months, hundreds of US military advisers sent to Iraq have compiled assessments of Iraqi military strength against Isis, a process that the Obama administration has portrayed as a prerequisite for any airstrikes. But with no offensive action taken, the Pentagon has faced criticism for dragging its feet on a deepening crisis.



Now Kurdish peshmerga irregulars have fallen back to positions closer to the regional capitol of the autonomous region, Irbil, following days of Isis gains in nearby towns in and near Iraqi Kurdistan. Tens of thousands of civilians are said to be crossing into Kurdistan for shelter. As much as the dire persecution of Iraqi religious minorities has prompted Obama administration discussions of food, water and medicinal air drops, the threat to the pro-US Kurds has contributed to the reengaged debate over air strikes.



An Isis incursion into Kurdistan would “change the strategic picture very, very significantly,” said Dave Deptula, a retired three-star US air force general who headed intelligence for the service and planned air strikes in Iraq during the 1991 war.



More than 11 years since the US overthrew Saddam Hussein, Iraqi Kurdistan has been an island of calm, even during the darkest days of the occupation and civil war. Motivated peshmerga, armed with rifles and driving unarmored trucks, patrolled makeshift frontiers and checkpoints, warning anyone who would ask about the necessity of preparing for new persecution from Arab Iraqis. Arab Iraqi notables would travel to Kurdistan for vacations, skiing and a respite from the chaos of war. When the Obama administration established two joint operations centers to merge US and Iraqi military planners, it placed one in Baghdad and the other in Irbil, meaning US advisers are not far from Isis fighters. Earnest, outlining Obama’s longstanding thinking about launching new air strikes in Iraq, noted that protecting US personnel was a core concern for the US president.



Deptula said providing the Kurds with air power was “a much easier decision than providing force to support Maliki’s regime” in Baghdad.

Christopher Harmer, a retired US Navy officer, said the speedy advances of Isis threaten to upend the peshmerga’s traditional strengths.



Against Saddam Hussein, “they were a classic insurgent force, with local population support, freedom of manoeuvre, able to live off the land. But now it’s Isis who are the insurgents,” leaving the peshmerga with the vexing challenge of defending and holding territory.



Any air strikes or humanitarian aid drops, both of which were under consideration during a Thursday morning national security briefing for Barack Obama, would likely come from the nearest air base, the Incirlik airfield in southeastern Turkey, about 400 miles from the starving Iraqi Yazidis that Isis forced up Mount Sinjar.



A major launch point for the 1991 air war against Saddam’s forces and the northern no-fly mission that continued until 2003, Incirlik is effectively the end of Nato’s eastern air-supply route. US defense analysts and former warplanners considered it the most sensible launch point for either strikes from manned attack aircraft like F-15s and F-16s and high-flying cargo planes like C-17s.



Isis is not believed to have air defense systems more advanced than 23 millimeter cannons, which cannot threaten US attack or cargo aircraft that can drop bombs or supplies above 30,000 feet. The range of the Isis guns would threaten helicopters –some of which the US has sent to Iraq, along with hundreds of US special operations “advisers” – and A-10 close-air support planes, but not the higher-altitude F-15s, F-16s or C-17s.



Surveillance drones, which the US flies more than 50 times daily over Iraq, carry 100lb missiles, but are most useful when aided by tactical controllers on the ground who can help spot for strikes. Drone strikes are more likely to take the form of discrete attacks than the concerted air campaigns that typically require fighter pilots.



Harmer said that while the special operators in Iraq are capable of retasking to support strikes, the US would be reluctant to place them among Iraqi security forces of potentially dubious loyalty.



“Who wants to trust their life to an Iraqi security force guy right now?” Harmer said, although many in the US military consider the peshmerga’s loyalties solid – although perhaps outpacing their capabilities.



The US also has had an aircraft carrier, the USS George HW Bush, in the Gulf since June, and access to a Gulf air base, Qatar’s al-Udeid air field. Navy cruisers and guided-missile destroyers in the Gulf carry Tomahawk missiles that provide a non-manned option. All of that provides Obama with options beyond Incirlik.



“Clearly Incirlik is one that has been very effectively used in the past and would most certainly be part of an effort to sustain support operations in the region,” Deptula said.



The 2002 congressional authorization to use military force against Iraq has never expired, even despite the 2011 US military withdrawal. Obama, whose administration formally favor’s the authorization’s repeal, can likely rely on it for legal cover should he opt for airstrikes.

A professor of international law and the University of Notre Dame, Mary Ellen O’Connell, said that the US needed no prior permission for humanitarian air drops, but air strikes would require a request from the Iraqis – which was provided months ago – and Obama would need to provide assurances over their effectiveness and proportionality against the Isis threat.

Deptula said the limited air-defense capabilities of Isis made a “competent, coherent holistic air campaign” a viable option.

“It’s a matter of the decision to put together such an operation. It’s clearly feasible but what has to be balanced is the endgame, the desired political outcomes, before we jump in with air options,” he said.

