In 1962, during the Cuban missile crisis, a US nuclear missile team received erroneous orders to launch. The commander of that team saw something fishy and verified they were sent by mistake, thus averting a nuclear war.

There have been many other near escapes, including that of the bombs that could easily have detonated when they fell over the US.

We can't rely on lucking out every time, so we can't regard the current nuclear deterrent situation as safe.