No, because their power is limited by their role in society and the organization in which they operate. Even the president of the United States has limited powers. If Obama just decided one day that the best course of action was to nuke Moscow and doubled down on doing so it's extremely unlikely he'd be able to do so. There are enough other people with careers, jobs, pension plans and common decency between him and actually launching missiles that I don't think it's credible that it would happen on a whim like that, even a persistent one. Someone would call a doctor and get the President some medication.

However, that depends on the people between the president and nuclear launch being decent human beings that care about law and order and proper procedure. You need to look at the system, not just individuals.

Alternatively, let's say someone came to power who genuinely believed nuking Russia was a good option. Rather than order a launch on the spot, what they'd actually do is gradually build a case, appoint pliable or similarly thinking people to key positions, get the launch protocols revised, engineer a geopolitical crisis by provoking Russia and drive events towards a situation in which a nuclear launch seems like a legitimate option.