Clint Watts (CWOT on SWC) asks if the USA is ready to again build-up Sunni (tribal) militias in Iraq and just maybe nearby - in the knowledge that their loyalty is only rented:http://www.fpri.org/geopoliticus/201...-against-isis#

It is not a policy problem just in Iraq:
The lack of viable ground options for securing terrorist safe havens is not a challenge unique to Iraq. The U.S. faces a similar challenge against jihadist enclaves enmeshed in ungoverned spaces in Pakistan, Afghanistan, Somalia, Libya and the Sahel to name only a few places.
He provides a framework summary:
Four factors: Establishing favorable conditions for negotiating with militia partners; Offering incentives for participation; Determining the level of control and responsibility for militia actions and Duration of Support
The use of irregular forces is very common in Western COIN and relatively recently in colonial wars in Southern Africa - sometimes with a persistent legacy, e.g. Mozambique.

The Iraqi Kurds know all too well that external support can be quickly terminated; those Algerians who served France paid a high price.

I am sure the prospective 'rented' militia manpower in Iraq know very well their options and that Daesh (ISIS) will be ruthless.