There was some kind of effort underway in the military bureaucracy to portray sending an additional 40,000 or so troops to Afghanistan as a “middle” option, but Spencer Ackerman points out that something in the 30-40k range is at the very limits of what’s logistically feasible:
If President Obama orders an additional 30,000 to 40,000 troops to Afghanistan, he will be deploying practically every available U.S. Army brigade to war, leaving few units in reserve in case of an unforeseen emergency and further stressing a force that has seen repeated combat deployments since 2002. […]
Obama would have something of a cushion, but not much, in the early months of 2010. An additional five brigades will finish their 12 months of so-called “dwell time” at home between deployments by April 2010, providing an additional 22,600 troops, but by that time, about 10,200 troops will be scheduled to leave Afghanistan, leaving available a net gain of 12,400. More brigades become available in the summer and fall, although others currently in Afghanistan will be ending their scheduled deployments then as well.
I don’t really think we need to worry too much about the possible lack of a contingency force to fight off an invasion from Mexico. But I think this underscores the fact that even though it’s annoying, from the point of view of a political observer in Washington, to see the internal administration Afghanistan debate drag on like this there’s no particular practical urgency to making a decision. The U.S. presence in Afghanistan has been scaled-up substantially in the two years, and further increases would need to be implemented over time.