The whole Russian establishment (not just “Putin”) is determined to prevent Ukraine becoming a military ally of the West against Russia, for the same reasons that the USA has always categorically opposed Central American countries becoming allies of outside powers actually or potentially hostile to the USA.
The Russian establishment is also increasingly concerned by Ukrainian state measures to banish the Russian language from the media, public life, government and higher education. They believe that over time this will destroy the historic cultural ties between the two countries and turn Russians in Ukraine into a despised minority.
The Russian government has not made up its mind to go to war, but it is prepared to do so in the last resort if it cannot achieve some kind of compromise with the West and Ukraine. The USA and the West are NOT prepared to go to war with Russia for the sake of Ukraine.
In these circumstances, it should be obvious that US policy should be dedicated to finding a diplomatic and political solution to the Ukrainian crisis. This solution in fact already exists, and has been endorsed by the USA and UN. It is the Minsk II agreement of 2015, negotiated between France, Germany, Ukraine and Russia, providing for autonomy for a demilitarized Donbas within Ukraine but guaranteed by international treaty.
To get this agreement implemented will require US pressure on Russia and the Russian separatists to withdraw their forces; but also on Ukraine, which has been very reluctant to guarantee real autonomy for the Donbas, fearing that this will block eventual accession to NATO.
This however is an illogical position, since as long as the Donbas conflict remains open Ukraine cannot join NATO in any case, and Ukraine cannot reconquer the Donbas without a catastrophic war with russia. So neither the West nor Ukraine would lose anything real by a settlement based on Minsk II.