I believe the general consensus is that nuclear war is a great risk and important to prevent but the effectiveness of philanthropic efforts is low. Fighting malaria is still a more effective form of altruism.

https://www.givingwhatwecan.org/cause-areas/long-term-future...

https://80000hours.org/problem-profiles/nuclear-security/

https://www.effectivealtruism.org/articles/carl-robichaud-fa...