What happens in Ukraine?

On the Russian side we have

1. A whacking big Russian army, and some Russian navy, camped out, in the snow, on Ukraine’s borders.  It would just take a telephone call from Putin to get them moving into Ukraine.  That’s at least twice, maybe more, the size of the Ukrainian army. 
2. Putin has the Germans, and plenty of other European countries almost hooked up to enough Russian natural gas to heat all their homes and run all their electric plants.  Putin knows (or he ought to know) that the Germans need that gas and will do a lot to keep the pipeline deal going, even if the Americans want to shut it down.
3. He knows Biden is mostly out of it, and even in his better days was not very brave, and will do nearly anything to avoid conflict.
4. It’s probably up to Putin alone, if he thinks invasion of Ukraine won’t cost too much he will do it.  If he thinks it will hurt Russia he won’t do it.  Unless we have another Oleg Penkovski (legendary sleeper mole in the Kremlin), we won’t know until it happens.

On the American side we have:

1. NATO and other treaties that give us a lot of support all over Europe.
2. Serious economic strength, far greater than the Russians have.  This strength would be better used if Biden made some straight forward threats of economic sanctions.