Here's a way for nuclear to make a dent: if the defense officials [1] who claim the climate change is a security threat are indeed serious about it, they could demand that Congress legislate the US military to be net zero carbon emitter. The US Navy can then build and operate enough reactors to achieve that. They already are operating dozens of naval nuclear reactors, and acquiring new ones at a steady pace (2-3 per year). Their regulatory hurdles are basically zero.

Currently the US defense emits a non-negligible amount of CO2 [2]: "If it were a country, it would have been the world's 55th largest greenhouse gas emitter, with emissions larger than Portugal, Sweden or Denmark." [2]

[1] https://www.npr.org/2019/03/05/700462955/former-defense-lead...

[2] https://www.livescience.com/65698-defense-department-climate...