Winter is the classic season for a Russian offensive. The ground is firm, rivers/streams frozen, and they enjoy a long history of of such campaigns. Anyone remember December 1941? November 1942? January 1945?
NATO will do nothing but wring its collective hands and hope the Ukrainians can stand essentially alone. Britain has promised and delivered some aid, as has the US, but President Prevagen will not commit the US to any direct conflict with Russia.
An interesting, if very unlikely "what if?" might be Poland entering the action in direct support. The Poles know they would be next within a few years (as do the Baltic States). They and the Lithuanians harbor a justifiable hatred of all things Russian, and perhaps the very threat they might get involved would be the only one that might make Putin think again.
A Polish/Lithuanian attack on Belarus would almost certainly put the fear of God into any Russian forces committed within Ukraine for fear of being cut off. Moscow would have to withdraw forces to support Belarus, pretty much ending any realistic hope of conquering Ukraine.
It is to be expected that Russian amphibious forces will attack Odessa in order to control that crucial port, if only to prevent any possible material aid being delivered to Ukraine in bulk. Kiev knows this, so must be trying to hold aircraft and the country's limited naval assets in a posture to allow them the chance of striking such an invasion force en route from Sevastopol.
It may be assumed that the US is sharing satellite and other intelligence with the Ukrainians, so when an invasion force puts to sea, their should be a chance to strike before reaching their landing zones. In the HIGHLY unlikely event the US was to get involved, our submarines in the Black Sea could make very quick work of such an invasion fleet, not to mention Sevastopol itself. But that would be direct involvement, and would mean we were firing FIRST.
Ain't gonna happen.
That said, the Russians will certainly try to open the show with air and missile strikes on Ukraine's air and sea assets in order to prevent any interdiction, so landings won't
likely begin until D+1 or 2.
Also, look for significant Russian airstrikes--after those initially targeting Ukraine's air force, fields, lines of communication, troop concentrations, etc--on population centers in the hope of cowing the populace to a quick surrender. The humanitarian crisis will be the worst in Europe since 1945.
And, yes, if the fighting looks like it will last a month or more, Taiwan will absolutely rise to the top of the "Other Shoe To Drop" list. Beijing and Moscow (not to mention Teheran and Pyongyang) KNOW the US will not become involved in a two front world war.
Public demonstrations/rioting here in the US against any involvement in either crisis will further paralyze a feckless government until such time as both wars are settled with essentially none of its vaunted military forces influencing their outcomes.
It is also at least possible that while Putin and Xi both need to strike in 2022 before the growing chance that a Republican/Conservative control of the Congress could interfere with his plans, they might have agreed to coordinate actions, virtually guaranteeing inaction by the West in general. They don't have to be friends to pursue their own lifelong goals when conditions for each are most favorable.
Once more, I hope I am so wrong on all this that I can be publicly shamed for it.
TVAG