If democratically-elected government disappears, something will fill that power void, and they will control that arsenal. Who knows what could happen with them.

they'll fight other countries to deflect from internal problems

The US is a major nuclear power and is one body that actively works to counter-balance nuclear proliferation in the world.

Not quite sure how to answer that if it's not already obvious to you. If democracy collapses, the result will almost certainly be Donald Trump being effectively a dictator. He very nearly started a nuclear war on more than one occasion during his first administration when some checks and balances were still in place [1] [2]. Nothing could stop him if he decided to do it again during his second.

[1] https://gizmodo.com/the-pentagon-worried-trump-was-about-to-...

[2] https://www.nbcnews.com/news/military/milley-acted-prevent-t...