Dianne Feinstein, like most people in the world, probably thinks US nuclear weapons are targeted at somebody's cities. This is not true — yet. I say not yet, because targeting cities is one of the moral hazards on the path to zero nuclear weapons. The current US policy (and probably the Russian policy as well) is counter-force targeting. Counter-force means targeting the adversary's nuclear and conventional military forces and assets. We can afford to do this, because we believe we have enough assets to survive a first strike and still deliver an effective counter-strike.
But at some point, as the US destroys its nuclear weapons, there may not be enough to target an adversary's forces. So, in case hostilities break out, we will have to target (hold at risk) something else the adversary values. This is called counter-value targeting. Counter-value targeting is aimed at economic and symbolic centers, which are usually co-located with population centers. Hence, counter-value targeting is effectively a euphemism for threatening to launch nuclear weapons at cities.
Depending on how the geo-political climate evolves as we proceed along the path to zero nuclear weapons, we may need to switch from counter-force to counter-value targeting. The question for the American public is whether this switch is compatible with their moral values, or whether it might be better under some circumstances to pause on the path to zero until geo-politics makes it safe enough to proceed without switching to counter-value targeting.
Besides our targeting policy, the other moral hazard on the path to zero is strategic stability. As our nuclear forces decline, do we disperse them so that a single strike cannot destroy them all? Or do we consolidate them so that they can be more easily guarded against theft and diversion by terrorists? If we consolidate, then we may have to "launch on warning," because if we wait for confirmation that nuclear weapons are indeed striking us, we will have nothing left with which to strike back. If we disperse, then we will need to have the will to spend resources on security measures - "guns, guards, and gates," etc.
We do not need to "commit to a nuclear free world," as Dianne Feinstein demands. By treaty, we have already done so. We need to have a sober consideration of how we might get to that world. It will not be as easy or as safe as many people assume.
See also: Folding the Nuclear Umbrella and Pitfalls on the Path to Zero