There is obviously no threat from Russia to Ukraine.
Well, here's the thing: a conquest can be divided into at least three substantially different stages:
1. invasion - when you send the troops to defeat the defending army
2. control - when you impose your rule upon the seized teritory (law, taxation, civil authorities)
3. assimilation - when Gauls start wearing togas and speak Latin
Russians have had their lesson in Afganistan, just like we recently had both in Afganistan and Iraq: you can swiftly crush the defending force using your overwhelming technological and numeric superiority, and still be forced to leave the country after some years of bloody, frustrating asymetric warfare, achieving nothing except for filling out pockets of the military industry with taxpayers' money and filling black bags with bodies. You need the hearts and minds of the invaded civilian population, you need if not their support then at least indifference to succeed.
So even though Russians may be confident that should they attack, they would have eaten lunch in Warsaw, diner in Berlin and breakfast in Paris, yet they still shall not invade, knowing that they have no means to establish the control over the teritory, not to mention the assimilation of the population. In other words: they could not digest what they could swallow.
Crimea had been only given to the Ukrainian Soviet Republic in the 50ties, as far as I can remember - it was done within the borders of the Soviet Union, so, for want of a better example, it was like giving Chepstow to Gloucestershire. Putin has a huge support among local, Russian speaking population, hence there are no hostilities against Russian army or ciilian authorities there. Yet the costs of "reuniting" Crimea with Mother Russia are devastating to the economy as Russia has to unify the infrastructure (think: financial services, telecoms, public transport, utilities, schools, etc).
The population of Eastern Ukraine is also by and large Russian speaking and culturally distinctive from Westen Ukraine, so they may or may not (depending on whose propaganda you believe
) be more in favour of integration with Russia rather than the EU.
Invading Poland, with practically non-existent Russian minority, millions of Poles remembering their basic training from the times before conscription was abolished plus some 100 000 para-militaries, eager to swap their AEGs to AKs (let us not forget, a substantial number of them actually legally owns assault rifles), 115 000 registered hunters and an indefinite number of farmers who stashed their granddad's PPSh and a couple of grenades in the attic, just in case - I cannot imagine what political purpose would that serve?
The war in Afganistan was one of the key factors which contributed to the fall of the USSR. Why Putin would consider another such disaster?
Well, at least this is why I think that we cannot extrapolate the situation in Ukraine to Poland.
