Saddam's henchmen, the main enemy, were no dummies. They were smart enough, and resourceful enough, to build a police state apparatus that kept Saddam in power for over three decades. However, for the last three years, that talent has been applied to keeping the henchmen alive and out of jail. But three years of fighting has reduced the original 100,000 or so core Saddam thugs, to a few thousand diehards. Three years ago, there were hundreds of thousands of allies and supporters from the Sunni minority (then, about five million people, now, less than half that), who wanted to be back in charge. Now the remaining Sunni Arabs just want to be left in peace. Thus the Sunni nationalists of in the Baghdad suburbs are shooting at, and turning in, their old allies from Saddams Baath party and secret police. This isn't easy for some of these guys, but it's seen as a matter of survival. While the fighting in and around Baghdad is officially about rooting out al Qaeda, and hard core terrorists, it's also about taking down the Baath party bankers and organizers who have been sustaining the bombers with cash, information and encouragement.
The Sunni Arabs were always the heart of the resistance to the new Iraqi government. They could not imagine Shias dominating Iraq and assumed that enough killing would put the Sunnis back in power. Their support was necessary to support Sunni resistance whether the Sunnis were Baathists, nationalists, jihadis, or foreign jihadis.
Increasingly, the Sunni fighters and terrorists are running out of friendly Sunnis to support their fight--they've run to Syria or Jordan or have switched sides recognizing that they were doomed to be defeated. The speed of their defeat is the big question, not whether they are beaten.
The Shia resistance based on Iranian-supported death squads, should be far easier to break since they are fighting a Shia government.
