a) the failure of the initial invasion to install a puppet regime in Kiev;
b) the failure of the current operation to conduct a Kesselschlacht destroying enough of the UA to force Kiev to sue for peace and leave Russia in control of the territories it has now seized.
The big question is whether Kiev will have the forces to shove the Russians out of much of the territory they now hold.
I'm pessimistic about Ukraine's chances of liberating much of Russian-held territory. Up till now the Ukrainians have tied up Russian troops in a deep defensive belt in the east while sending tank hunting teams to destroy Russian armor and generally demoralize the Russians. The Ukies turned out to be pretty good at this. But it now seems that the Russians are holding most of the territory south and east of the Dneiper River and are going over to the strategic defensive. So now the shoe is on the other foot. UA has to attack prepared defensive positions. And they already appear to be on point of mutiny.
“The big question is whether Kiev will have the forces to shove the Russians out of much of the territory they now hold.”
The companion question is whether Moscow will have the forces to hold the stolen territory. They’re hurting economically and the ironic fact of their military equipment is that much of it was built in Soviet-era Ukrainian factories that have now been destroyed.
Most of the equipment Russia is losing in this war cannot be replaced. Russia can’t do it and China has made clear they won’t sell any kind of vehicles to Russia. So after they run out of tanks and BMPs they’ll have nothing.
Right now Ukraine has to hold the line and as Russia goes broke they’ll be able to push the invaders out of Ukraine and they’ll inevitably retake Crimea.
And at the point the Russia-Ukraine War concludes is when it would be most advantageous for China to invade Siberia. Russia will be at its weakest, they will not be able to obtain resupply, and the world will not give one single care that China is taking back what the Russians stole from them.