russia is a big country US cannot keep it..
from weapons and technology and war knowledge usa can do the job it will take long and will end blody they have to keep the moral high but I think that would be the biggest problem in a war with russia..
winning is one thing but occupy it and hold it for longer time another..
if we take just russia with usa and without sanktions and other stuff.. just the two
than US will win if they want to...
the problems are:
massiv death for both in own land for us it would be new and could shock them
or help one side a little bit with weapons informations little support for russia could make the war longer and more longer they fight the longer china can rise up