the united states is not going to war over ukraine. the united states SHOULD not go to war over ukraine.
ukraine is not a nato member and we owe it nothing. when we go off on our little dalliances to "defend democracy" we get ourselves in trouble. (and ukraine isnt much of a democracy anyway...freedom house gives them a lower ranking than (gasp) hungary with evil orban...even though freedom house is bullshit)
we have a set of solid alliances that we need to respect and defend. israel, nato, japan, south korea, australia, canada!. other than that, we can pick and choose our battles in the new cold war. ukraine is not in our interests and should not be a red line in any sand.
russia will not invade a country that is a member of nato. the us can use the ukraine as an excuse to bolster up some defenses in poland and the baltics to make them feel better, but it should not be fighting russia in the ukraine.
i assume this is biden playing bad cop to europe's good cop to try to strike some deal that will leave russia holding the cards on ukraine without formally invading it.