Strategypage writes that Russia's military just isn't up to the task of invading Ukraine:
Russian threats to use military force against Ukraine are largely bluff. ... Despite increasing defense spending by a third since 2008, less than half the troops have modern (post-Cold War) equipment. ... Worse, a third of the [300,000] Russian army troops are conscripts, who are on active duty for one year. ... Russia has less than 100,000 [army] (and less well equipped and trained) reserves. Russia also has 200,000 armed men in the Interior Ministry. This is basically a paramilitary forces equipped as light infantry. ... A third of the Interior Ministry troops are conscripts. ...
[Russian] officers note that since 2008, when the five day Russian invasion of tiny Georgia exposed the equipment and training shortcomings of the army, not a lot of progress has been made to remedy those problems. Russia only has about 100,000 paratroopers, commandos and airborne troops it can really rely on and these elite forces have to be ready to deal with emergencies across the vastness (11 time zones) of Russia. Those hundred thousand troops would be quickly tied down if a similar move were made into Ukraine (which has ten times the population of Georgia and much more capable armed forces). Russia went into Georgia with 20,000 troops, about a third of them pro-Russian irregulars from nearby areas that had grudges with Georgia. That force suffered higher losses and a lot of other unexpected problems.
Do read it all. Sure, Russia can dispatch some aircraft to Belarus as a visible counter to our small deployment of F-16s to Poland, but Russia's response is just as symbolic. Although Belarus' dictator Lukashenko's description of our small deployment as "large-scale exercises" is an unfortunate (and wrong) description that needlessly heightens tension.
This is why when I speculated about a Russian invasion of Ukraine, I focused on a real invasion of just Crimea, while speculating that operations in the rest of Ukraine would have to be limited to eastern Ukraine. And that even that would have to be limited to essentially a lightly opposed road march into urban areas.
IJust because the threat of invasion is "largely bluff" doesn't mean Russia could not invade Ukraine. But it would be ugly and lack "style points" that are required when a major power uses force against a minor power. Especially given Ukraine's unready military, I think Russia could bulldoze their way into eastern Ukraine over Ukrainian opposition.
But it would be ugly and expose Russian weaknesses. Russia doesn't want that.
And if Ukrainians resist such an invasion of eastern Ukraine, Russia could face a long front line against Ukrainian troops that attempt to whittle away Russian control while partisans resist in areas of Russian control.
Although obviously, Ukrainians can rightly want to avoid a war even if they believe that ultimately they will eject the Russians.
I think Russia really doesn't want to attempt more than Crimea. That's at the limit of their real power, I believe. And even that could look ugly if the Ukrainians resist in their besieged bases and if Ukraine can use (even if it burns up) their small air force and navy to exact a price and deny Russia easy style points.
Heck, if Ukraine uses even their 6,000 troops identified as effective with as many anti-aircraft missiles as they can push forward, perhaps they could recapture some of Crimea near the neck (and pour more troops into the urban areas where they have the easier task of simply holding in place) before substantial Russian ground forces could get there. Even if the Ukrainians just take the Armyansk region, that makes Russian defense of the peninsula more difficult by giving Ukraine a jumping off point for a future liberation.
As I noted, if the price of conquering even just Crimea can be made to be high enough, could we get Russia to accept just ownership of Sevastopol? Sure, it is purchase under duress, but it is an exchange of something Ukraine isn't prepared to deny Russia, anyway.
Before we get too focused in making Russia pay a price for conquering Crimea, we need to make efforts to stop the Russians from taking Crimea. Remember, although Russia has built the backbone to achieve the control of Crimea, the Russians don't actually control Crimea yet.