He knows Biden wouldn't risk war over Ukraine, and he knows Biden won't fight without NATO, and he knows even if he did, there's no way NATO could win it without going nuclear. The threat of invasion by itself would probably get him what he wants, which is to intimidate Europe. The problem with that reasoning is he doesn't know for sure Biden and NATO WILL back down--they may decide to fight and threaten to go nuclear. If that happens, all those troops and ground superiority won't do him any good, and he will have no option but to go nuclear himself. At that point, all those troops and materiel will be of little value. Russia has big and well equipped armed forces, but it doesn't have the industrial might to take on all of Europe in a protracted conventional war, especially one that the Europeans and Americans, whether correctly or not, decide they can't afford to lose.

Hitler made the same mistake in Poland. He knew the Brits and French were in no position to stand up to him, but they decided to do so anyway. From that point on, his enemies, regardless of how weak they might be, had a vote in the outcome.

That's the problem with starting wars, even if victory is certain, you have no guarantee the losing side won't care and will do something really stupid. Like the Fat Man told Sam Spade in the "Maltese Falcon"; "Such situations require the greatest judgement from everyone involved because in the heat of action, men tend to forget where their true interest lies." And in today's high tempo military environment, the situation can quickly get out of hand.

The same problem occurs in WESTPAC. The Chinese are stronger than the US and its allies in theater, but eventually the US can muster bigger forces. from the rest of the world. If either side finds itself in a jam, the nuclear option is the only way out, and it is too easily available.

Remember what Pyrrhus said after he defeated the Roman Legions. "Another victory like that and we're finished."