Ignoring the lessons of the total withdrawal from Iraq about 2-1/2 years ago--and add the lesson that nearly 60 years after World War II the Europeans are unable to defend themselves without our help, the Obama administration will slash the amount of troops we will keep in Afghanistan after this year:
The decision to consider a small force, possibly less than 5,000 U.S. troops, reflects a belief among White House officials that Afghan security forces have evolved into a robust enough force to contain a still-potent Taliban-led insurgency. The small U.S. force that would remain could focus on counter-terrorism or training operations.
I think even a bit more than 10,000--which had been the number tossed around--is insufficient for the first years. I'd like a complete infantry brigade on the ground to hold a "base star" as a hard target, backed by artillery and air power, if things go really bad and we need a place where Americans and other Western troops can seek refuge should a wave of Islamist rage sweeps across the place.
Five thousand is just enough to provide the raw material for a really good massacre body count without being enough to defend itself.
I thought ten thousand was a number designed to provide an excuse that the Obama administration tried to win. Five thousand doesn't even provide plausible deniability that they don't care about winning the "good" war.
UPDATE: Thanks to Pseudo-Polymath for the link.