I count that under "decides that escalation is a risk they're willing to take". We can all see the claims and threats made by the Russian government, we know they want us to fear their nukes, that's why the US government has been concerned about escalation.
I personally think there's a 75% they can't use any of their nukes and a 92% they can't use a strategically decisive number of nukes.
But I'm doing armchair analysis here, and even if I wasn't those odds are only sufficient for me privately to not worry, they're not enough for a government to not plan for the worst. I'd be more worried if the US was more hawkish and cavalier about this.
Though that's even assuming Putin (etc.) actually tries to use them — as I said, Biden's deliberately not given enough aid for Ukraine to win hard precisely because he doesn't want to risk it.
He's limiting support to enough to not lose, which is different than winning; he doesn't want Russia to keep rolling tanks to the line of the old Iron Curtain either.
