Comment by SlinkyOnStairs

The problem with nuclear deterrance is that it is a game theory divide-by-zero error.

For a state like Ukraine, whether they retained their nuclear weapons is irrelevant; They'd never use them against Russia because the retaliation will always be more severe, whether they target Moscow directly or mere "tactical" use, Ukraine would lose the nuclear exchange.

And Russia hasn't used it's nukes despite Ukraine not having any nor being under anyone's nuclear umbrella. The threat of sanctions has (thus far) been sufficient.