Re WWW 3
Things could easily spiral out of control. Look at the shyte storm right after pieces of a Ukrainian anti air missal landed in Poland with 2 dead. Imagine what would happen if it was a defective Russian cruise missal that blundered into Poland and landed in one of their cities killing hundreds. Everything that the USA has done has been carefully calibrated to try to avoid going up the escalatory ladder. Avoiding WWW3 is job one for Biden.
Failure in Ukraine means failure for Putin. It is not unreasonable to think that this puts Putins life in danger. If you think you are going to get killed when you are overthrown where is the downside in starting WWW3 ?