Obama is boxed in by his own rhetoric on Afghanistan. While running for President, in order to look tough while condemning Bush's war in Iraq, Obama made comments to the effect that Afghanistan is the real war we should be fighting because that's where al Quaeda is located. So it would be precipitous for him just to pull out now. He would look weak, the last thing any Democratic President needs. There may be legitimate reasons for keeping a miltary prescence on the ground in Afghanistan, but for the most part they escape me. They seem to boil down to "al Quaeda might come back." Well, yeah, and then again they might not. They may go elsewhere like to Somalia, for example. Is it worth sending young people into harm's way on a "maybe"?
I think, as much as I hate to say it, that Obama's decision to send more troops is all about political calculations. First, Obama is turning out to be an avowed centrist. He doesn't want to do anything too radical at least during his first few months in office. Leaving Afghanistan abruptly at this time would be too radical. There is too much on his plate here at home to have to deal with a firestorm from the right about leaving Afghnaistan abruptly. He would like to get health care passed. He would like to do something about jobs. Better to let Afghanistan remain at the status quo than to have to deal with another firestorm from the right, another distraction from his main goals. And it would give Republicans additional ammunition in the upcoming congressional elections of 2010. Better to neutralize that by remaining in Afghanistan, and there is always the possibility that something can be improved there, but I doubt it.
Besides he can always pull a Nixon, declare victory and pull out of Afghanistan just before the 2012 election. At that point Obama will look pretty good if 1) a substantial health care bill has been passed, 2) the job situation has substantially improved and 3) he has just completed a successful war in Afghanistan. Why not pull a Nixon and use the ending of the war as a tool to get reelected? Nixon promised to end the Vietnam war, he hinted that he and Kissinger had a "secret plan," but conveniently let it drag on until just before the next election which Nixon won handily only to be tripped up by Watergate a few months later. This sounds cynical, I know, and in Nixon's case the cynicism is certainly justified. But Obama cannot survive in office without making political calculations as well, particularly when that's all the other side is doing. If the Republicans ever do anything except from political calculations, it will be news to me.
Obama has already set the groundwork for withdrawl from Afghanistan with his announced exit strategy which gives McChrystal 15 months to get things done or else. That would put us into mid 2011 just a few months before Obama would be revving up his reelection campaign. How convenient! My prediction is that he will declare victory at that time and pull out. Better to have the firestorm from the right then as part of a referendum on his reelection campaign than to have it as another distraction now. Besides ending the war then will leave the Republicans - if they should replace him in 2012 - without an ongoing war which they would dearly love to inherit from him. If Obama wins in 2012, it leaves him with a clean slate for his second term during which he can take a more radical stance on a number of issues since he won't ever have to deal with another election campaign. At that point he would have a shot at making a major change in the Weltanschauung or zeitgeist of the country, the way Reagan did, but in the opposite direction.
So there are many advantages from Obama's perspective for continuing the war in Afghanistan at this time both geopolitical and political. Of course, all calculations of this sort can turn out to have been unfounded. Things can go awry. The war, as wars are accustomed to do, could turn dirtier and messier. The economy could get worse instead of better making the expenditures in Afghanistan seem like an even bigger waste of money than they already are. Obama could end up being boxed in by reality and not merely by his own rhetoric.