Charles Krauthammer today credits the Iraq War with having damaged al Qaeda:
Iraq, too, was decisive, though not in the way we intended. We no more chose it to be the central campaign in the crushing of al-Qaeda than Gen. Dwight Eisenhower chose the Battle of the Bulge as the locus for the final destruction of the German war machine.
Al-Qaeda, uninvited, came out to fight us in Iraq, and it was not just defeated but humiliated. The local population - Arab, Muslim, Sunni, under the supposed heel of the invader - joined the infidel and rose up against the jihadi in its midst. It was a singular defeat from which al-Qaeda never recovered.
Slight problem here, though. The Council on Foreign Relations gives us the history of al Qaeda in Iraq (AQI) and well, er, um, it's really not quite so clear that AQI was a part of al Qaeda that existed prior to the invasion of Iraq.
Ahead of the 2003 invasion, U.S. officials made a case before the UN Security Council linking AQI with Osama bin Laden. But a number of experts say it wasn't until 2004, when Zarqawi vowed obedience to the al-Qaeda leader, that the groups became linked. "For al-Qaeda, attaching its name to Zarqawi's activities enabled it to maintain relevance even as its core forces were destroyed [in Afghanistan] or on the run," observed (PDF) al-Qaeda expert Brian Fishman in 2006. Fishman, formerly with the Combating Terrorism Center at the United States Military Academy, says the relationship eventually broke down when Zarqawi ignored al-Qaeda instructions to stop attacking Shiite cultural sites.
Sorry Charlie, but your theory's a bust. Had there not been an Iraq War, there never would have been an AQI. The defeat of AQI was hardly a defeat for al Qaeda.