President Bush has abrogated his role as Commander in Chief by letting Gen. David Petraeus choose the troop levels in Iraq, Afghanistan, and also the reserves at home.
Gen. Petraeus effectively chooses troop levels for everywhere else by choosing the troop levels in Iraq, which he is responsible for. This leaves little or nothing left over for anything else.
Afghanistan is where the 9-11 hijackers came from. They just had the biggest opium crop in history. (If you controlled the land, you could stop this.) We seem to be at best at a stand off. And nearby Pakistan seems to be becoming more violent.
We have rumblings of a possible war in Columbia. Suppose we want to support them. Would we have anyone to send?
On the other hand, as Bush claims, things seem quieter in Iraq. There are probably less than 1,000 al-Qaeda types left and they have little territory. Every ethnic group is opposed to them. They have no chance of taking over the govt. Why do we need 140,000 troops + Iraqi troops and police to go after them?
What Bush is not admitting is that he does not need a military victory. He needs some sort of political victory that will take his vision of Iraq forward. That's not likely to happen for a long time and there are major priorities elsewhere.