The only way to win a nuclear war is to not start one.
Now, it is my basic belief that the world leaders know this. In the history of nuclear weaponry, only two have been used in an offensive capacity. Those two were obviously "Little Boy" and "Fat Man", used at the end of WWII against the Japanese. Think about this in perspective; it has been sixty years since a nuclear weapon has been used. With every passing year, the threat of total annihilation becomes less and less plausible.
And not only has M.A.D. (mutually assured destruction for those of you too young to remember the Cold War) ensured that there hasn't been a nuclear war between nuclear capable nations, it has also ensured that there hasn't been any war between nuclear capable nations. I am convinced that one of the primary reasons that the Cold War never resulted in an actual land invasion was the threat of nuclear weapons.
On top of that, no one has used nuclear weapons in wars against non-nuclear nations. We could have glassed pretty much all of Vietnam, North Korea, Afghanistan, and Iraq and still had enough arsenal left over to destroy everything else. Afghanistan went to war with both the United States and the U.S.S.R. and didn't get bombed!
1) No one uses nuclear weapons
2) Nuclear weapons help deter non-nuclear war
What's not to love?
(If someone who doesn't care about their own existence or feels that the destruction of their enemies is more important than their own survival gets a hold of nuclear weaponry, that could be bad, because M.A.D. does not apply. Luckily, nuclear weapons take a lot of science and funding to build.)