They know that there is no precedent for such violence against them specifically. But they are also extrapolating, correctly I think, that people will want to kill them for what they are planning to do, above even what they are currently doing.
They had to begrudgingly push out the New Deal because they knew that a violent socialist revolution where the owners get strung up from their own chandeliers was the probable alternative.
Now they probably think modern security and propaganda will prevent all that, or they're just ignorant, shortsighted, and greedy, and they haven't really considered the consequences.
Declaring war is a boring, formal process that acknowledges authority other than himself, of course he doesn't want to do it. Why do all of that when he already has the thrill of ordering the deaths of random civilians and having the footage streamed live to him while he scarfs down a McDouble? If he wants to send in a Marine division he'll just say go do it, who's going to stop him?
The Russian state has stirred up a strong and very irrational national-ethnic hatred of Ukrainians from what I've seen. Their continued resilience is an insult to Russian pride and chauvinism, so the nationalist will pay heavy costs to try to make them kneel. If there's criticism, it's that the leadership is not killing Ukrainians competently enough, not that killing Ukrainians or going to war is wrong.
Like that racket they tried of getting teenagers to firebomb the Ukrainian diaspora in Europe. Completely strategically irrelevant, and could only be motivated by hatred.
They know that there is no precedent for such violence against them specifically. But they are also extrapolating, correctly I think, that people will want to kill them for what they are planning to do, above even what they are currently doing.