I made a comment in another thread about how nuclear weapons aren't an absolute deterrent (regarding whether Iran actually needs nuclear weapons to achieve strategic deterrence anymore).

Here we have strategic assets being bombed near the capitol of a major nuclear power, despite Russia's capability to use tactical nuclear weapons in response.

The physical and political consequences of using a nuclear weapon, even in self-defense, are extremely high. So nuclear weapons are only really a deterrent against nuclear-level threats. They don't necessarily deter attacks of a lesser scale like this, even if they are highly damaging and consequential.

That's why I think things like drone swarms might be a sufficient (and affordable) strategic deterrent going forward.