I agree with Patrick. You can't win the war on terror, at least not entirely. There will always be terrorist groups somewhere in the world.
I don't really know if there is any criteria to go by. And to be honest, I'd feel much safer today if we were at the stage we were before the Iraq war.
This is probably a good question to again in a year, since things will be unstable for years to come and opinions may change as the terror gets "close to home."
However, not to abandon all hope, it is possible that we can greatly diminish it and still strive for a safe world. Of course, it takes good leadership for that to happen, if you get my drift. :p
TIS