Following up on a cover story he wrote for Mother Jones last year, Peter Bergen has a new piece in Foreign Affairs on how Iraq has become a training ground for the next generation of international terrorists, just as Afghanistan was in the 1980s. It's a pretty well-trodden argument that has gained increasing empirical support of lateespecially with this report that many Saudi fighters only decided to take up arms after the invasion of Iraq. Bush has downplayed this thesis by arguing that it's better to lure all the terrorists into Iraq and kill them there than to let them lurk in the shadows abroad. But that assumes a) there are a finite number of terrorists out there, which we know is false; b) that the military can kill all of the foreign fighters that come to Iraqthey can't; and c) it ignores the fact that many potential terrorists are gaining much-needed training in Iraq, which was unavailable to them before.
Bergen also avoids the thorny question of whether and how U.S. withdrawal from Iraq would affect all of this. On the one hand, getting out of Iraq as soon as possible would stop the flow of aspiring mujahideen who are going to Iraq and learning how to kill lots of people. Plus, there's no way the U.S. can stay and kill every last newly-minted terrorist in Iraq, so it's fallacious to argue that "we can't possibly pull out or else all those trained fighters will go cause havoc elsewhere." Even if the U.S. pacified Iraq, those fighters would still escape and, potentially, go cause havoc elsewhere. But on the other hand, if the U.S. did leave Iraq and groups such as al-Qaeda and Zarqawi managed to take credit for the defeat, it is likely that they would gain a tremendous amount of newfound legitimacy, and the influx of funding and recruits that come with itjust as happened to Hezbollah after that group took credit for Israel's unilateral withdrawal from southern Lebanon. From a national security standpoint, that's not appealing either. At this point, basically, there just aren't many good options.