There was someone who worked in Washington who made a proposal that the nuclear launch codes should be printed on a little capsule that was surgically implanted inside a man who would travel around with the president, in kind of the same way that the briefcase or whatever-it-is travels around with him under the current system.
The deal was, if the president wanted to launch a nuclear strike, he had to take a big knife and kill the man to cut him open to get to the capsule. Kind of come to grips on an individual level with what he was dealing with, and what it meant on at least some level, instead of just pushing some buttons in an air conditioned office.
I don't think this was ever meant as a serious proposal. The person who invented it was just trying to make a point. But it did get relayed to at least one person who worked in the Pentagon who got very upset at the idea and started arguing against it. What if, he said, the president looks at what's in front of him and can't do it. That would be terrible.
I dunno I mean it's a pretty different proposal to logically come to the idea of like. oh something that's an existential threat needs to be nuked, whether that be like, godzilla, which is NOT a good idea, or like, just ensuring MAD because fuck it, I guess, or like, north korea or something, right, there's a difference between that, which should probably be a pretty cold and calculated decision, and like, killing someone, presumably that you know quite well after travelling with them for you know, at most, eight years, and then rooting through their corpse to find a little code with what's probably a time critical objective. I think probably, as another commenter pointed out, you would want to elect the president that can't kill a person. That's a better president, than the one that can, probably.
Bigger hole than all that, though: the president would probably just ask the secret service to do it, and the secret service would probably comply.