How Al Qaeda in Mesopotamia has managed this unlikely turnaround — from a near spent force to a reinvigorated threat to Iraq’s democracy in a little more than two months — is a puzzle to both the Americans and Iraqis who study the insurgent group, some of whom now wonder whether the organization in Iraq can ever be entirely defeated…

Perhaps as significant, Al Qaeda in Mesopotamia, an extremist Sunni group that believes Shiites are heretics, has recently begun to partner with Shiites in the county’s south, according to Iraqi officials and Awakening Council leaders who retain ties to the insurgent group.

The group has paid Shiites to provide intelligence and to manufacture and plant bombs in areas where a Sunni would most likely attract unwanted attention, said Abdullah Jubouri, an Awakening leader in Salahuddin Province, in northern Iraq…

The group, thought to be made up almost entirely Iraqis because the stream of foreign jihadists into the country has been cut to a trickle in recent years, is overseen by its third generation of leaders, who by all accounts are as ruthless as their predecessors, and possibly more cunning and capable.