Prevent the President from being able to launch a nuclear first strike on his own.
Why is this important?
I do not think any president should be allowed to launch a nuclear first strike with only the approval of the Secretary of Defense. I think at least a small, impartial group should have authority to block that decision. I also think someone like President Trump is likely to use this option, as he is too impulsive, and its consequences would be nothing short of disastrous for everyone on the planet.
