Supply their troops right across their border? Where do you think ukraine is? The side that will have problems with supplies is the one that had their armories, oil refineries, storage facilities, etc destroyed.
> maintain presence
Something they've done for centuries? They don't have to maintain a presence. The ukrainian army will. Notice how there aren't any major battles? Ever wonder why Zelensky is asking the civilians to fight? Because most of the ukranian army is not fighting.
> that is a very expensive operation in a country that really doesn't want you.
Half the country is russian to begin with. More than half the country voted to align with russia. That's why the West staged a coup.
> Extra hard when it's cold you have no food and you're running out of fuel.
It's only going to get warmer and Russia is not going to run out of food nor fuel. You do realize russia is the largest fossil fuel producer right?
> Vehicles are being abandoned and there is plenty of evidence for self sabotage.
Then how come major ukrainian cities are under seige?
Read what you wrote and ask yourself, is it really what's happening or is it what you wish was happening? I don't think the ghost of kiev is going to save ukraine. Unless a major power steps in to help ukraine, it'll be "liberated" in the next few weeks. And then ukranians will go on with their lives. No country is going to step in to fight russia.