One of the less-amusing peculiarities of the Bush administration is their relative lack of interest in nuclear proliferation. Nuclear proliferation is a question in itself, independent of terrorism, but one of the biggest fears about terrorism is that they might get nuclear weapons someday.
Beyond that, nuclear proliferation is intrinsically destabilizing. A world with 12 nuclear nations would be many times more dangerous than a world with the present five-to-seven.
Nuclear proliferation is a wonk issue which isn’t going to win any votes in Philadelphia, Mississippi. There are certain countries you want to look at very closely (e.g., Russia, N. Korea, Iran, and our new non-NATO ally Pakistan), and there are others which are not really involved (e.g., as it happens, Iraq.) There are various things you can do about nuclear proliferation, but it’s mostly low-profile stuff that doesn’t involve blowing shit up.
Furthermore, if you’re a national leader who feeds on public hysteria, nuclear proliferation is actually a good thing, sort of like Abu Mussab al-Zarkawi, since it can be used to justify whatever it is that you’re planning to do.
So it’s not surprising that Bush is not very interested and that Kerry is. Because Bush doesn’t have time for that wonk shit, and Kerry does.
The above is my opinion. Go to the link for what the Kerry campaign has to say.