In your opinion, when would the War on Drugs be won? Isn't that the real question?
When drug use stabilizes at some level for some period of time despite increased government spending, enforcement, and penalties, then I would say the War on Drugs has accomplished all it can. That doesn't mean we "won" or "lost" or even that the WOD is over.
I think we were at that point in the early 90's, prior to state decriminalization and medical marijuana legalization.
We need to recognize that there will always be some level of illegal drug use, just as there is with any other crime. That realistic attitude, however, does not make for a good campaign slogan.