Ukraine Crisis What I think is driving US foreign policy in Ukraine is the following:
1. Russia and Europe are in prime position to benefit from a war between the US and China.
2. Russia and Europe will both fill a critical role for China in said war, since China will need markets it can reach over land when its sea routes are blocked. Note that conflict in Iran and Eastern Europe would seal Europe off from China entirely.
3. European populism threatens to slip Europe from Washington's grasp, turning it from a vassal into a potential rival. (In terms of potential, Europe even surpasses the US and China)
So, being the United States, what do you do?
NATO will be useless in a conflict with China, especially if the Europeans start thinking for themselves.
You look for a way to leave NATO while simultaneously getting your two rivals (Europe and Russia) to fight each other.
A hypothetical scenario (not necessarily the most likely, but just to show how easily one can imagine this escalating):
Trump becomes president, and leaves NATO. With the US ditching Europe, European war paranoia will spike - keep in mind the Ukraine war may still be going on. This creates opportunities for trickery. A false flag attack on a base or ship, an assassination of some high-profile political figure, etc.
Wars have been started over less, and it wouldn't be the first time the US fabricates a casus belli.
Of course the US doesn't intend to be involved in this conflict at all. It will be its parting gift to Europe.