It's some phone calls to get the ball rolling. Whether or not various operators of nuclear ICBMs follow through, only one nuke is all it'd take to really massively change the world.
There's a playbook that has to be consulted, and target(s) selected. Of course it's not a terribly complex process, because the assumption is that a strike would have to be ordered without much notice. And that's also why the "nuclear football" containing everything necessary is always very close by the President.
But it's still far from "literally the push of a button."
Once someone who’s authorized to order a strike, e.g. Putin, gives the command (“presses the button”) - what else would Putin need to do for his command to be carried out?
My guess would be he doesn’t need to do much, and that the “risk” would be someone down the chain of command refuses to carry out the order.
