While there is a chain of command that could potentially stop a rogue president from unilaterally ordering a nuclear strike, at the end of the day the POTUS has an immense power in his ability to order a nuclear strike.
This whole nuclear strike thing is a canard, nobody is going to nuclear strike anybody. Yes, there's a chain of command, and also Trump is not some Hollywood supervillain. He is a real estate developer, a conman and a blowhard, not a Doctor Evil. So we need to stop discussing Hollywood scenarios and start discussing real issues the country is facing.