What the regular Iraqi military is incapable of doing. And, what weaponry the militia has probably was stolen from government forces – or bought from them. We sure left behind a stable government, didn't we?
The participation of the Shia militias in Iraqi military operations feeds the Islamic State’s propaganda and aids its recruiting. The Islamic State tells Sunnis that the Iraqi government is a pawn of the Iranians. The presence of organized Iranian-backed Shia militias in military operations in Sunni areas supports the Islamic State’s narrative.
Full story @ Sadr’s ‘Peace Brigades’ prepares for Mosul offensive | The Long War Journal