HR 669 law that prevents Trump from starting a Nuclear war. War may only be declared by Congress. The thing is Congress would have to pass this law.

The 25th amendment is to slow cumbersome and unwieldy requiring Pense and 14 cabinet members to line up against Trump.

Then who could stop WWIII ? https://www.vox.com/world/2017/8/11/16126770/trump-north-korea-nuclear-launch-code-steps