The text of the document found in the building where al-Zarqawi was killed is revealing, and it explicitly affirms Bush's policy of resolute refusal to cut and run and absolutely demolishes the Democrat rationale for a premature withdrawal. The text can be read here.
The short version is that the insurgents acknowledge that they're being worn down and degraded, the American strategy is working, and the best thing we could do, from their point of view, is to follow the advice of the "Last Helicopter" wing of the Democratic party and begin to withdraw. Since Bush is not likely to do that the next best thing is for al-Qaeda in Iraq to instigate a war between the U.S. and Iran to divert our resources out of Iraq and relieve the pressure on the insurgents.
The terrorists are on the ropes, and the Murtha, Pelosi, Kerry crowd, desperately fearful that Bush will succeed and be hailed by the public for his achievement, are riding to the terrorists' rescue with demands that we get out before they're absolutely defeated.
Read the insurgents' reasoning and the strategy laid out in the document at the link.