Putin can’t allocate all the forces for one campaign in Ukraine and leave the back door open near Japan, China, and Korea, the front door open near Poland, and the roof open in the arctic. Russia has its military broken down into regional defense vs expeditionary forces in general terms.
I tried to pull up an excellent German site resource where you can literally zoom down to the sub-unit level on an interactive map of Russia, but their site is 404’d. Called GFIS.org I tried with multiple VPN locations include "neutral zones” that park a lot of Russian offshore cash. Here’s an older screenshot of GFIS, so imagine just being able to zoom down to any operational symbol for a unit, whether it be Air Forces, Ground Forces, Naval bases, etc.
Russia is already a near-impossible territory to defend even with 100% strength on its best day. Putin has thrown sufficient forces at Ukraine if the objective is to not effect massive collateral damages, which makes sense because once the territory is taken, as much of the infrastructure will be necessary to harness in order to support Russia’s economy with flow of the resources.
With a pre-invasion population of 43 million people, it’s not like they are going away somewhere. Another problem is moving in ethnic Russians, since there aren’t enough of those in Russia as it is.
You also can’t rape the Ukrainian women as a military strategy to produce loyal sons as in the past, in today’s world. As long as Putin can stabilize things after the invasion, keep the oil pipelines flowing, stabilize the conditions of the sea ports, and keep the crops going with a hungry Chinese trade partner eating every kernel of grain possible, it will have secured Russia’s interests for the short-term.
The wildcard will be how Ukrainians adapt to being occupied when they just were conducting democratic elections and moving closer to Eurozone trade-all gone now. Putin could throw them a curve ball and say, “Nye problyem. Kanyeshna trade with EU, but of course you have to pay a little off the top to daddy in Moskva."
That will then show how impotent Biden is though. A recent poll said 52% of Americans don’t think Biden will run for reelection. Now that China and Russia have the voting machines all primed up, the mid-terms will be interesting to live through.