Considering how some of our Republicans behave in terms of blaming the opponent for misdeeds done by themselves, the scary scenario is that Russia has made or is making a dirty bomb designed to look like an enemy improvisation.
Using it (especially in a population center, like Belgorod or Simferopol) and then screaming about Ukrainian wmd use could possibly be the way Russia justifies retaliating in kind. And since Russia (a civilized nation unlike the feral Nazis they are fighting to expel from a breakaway republic) has none such, the only proportional response necessarily means using one or a few tactical nuclear weapons on or near the battlefield.
I hope I’m very wrong.