George Will nails it:

This will not end well – washingtonpost.com

Obama’s surge will bring to 51,000 his Afghanistan escalation since March. Supposedly this will buy time for Afghan forces to become adequate. But it is not intended to buy much time: Although the war is in its 98th month, Obama’s “Mission Accomplished” banner will be unfurled 19 months from now — when Afghanistan’s security forces supposedly will be self-sufficient. He must know this will not happen.
….
George W. Bush waged preventive war in Iraq regarding (nonexistent) weapons of mass destruction. Obama is waging preventive war in Afghanistan to prevent it from again becoming “a staging platform for terrorists,” which Somalia, Yemen or other sovereignty near-vacuums also could become. To prevent the “staging platform” scenario, U.S. forces might have to be engaged in Afghanistan for decades before its government can prevent that by itself.