[Webstral]

The Crimea is now Russian, for all intents and purposes. At this point, that situation can only be reversed by force of arms.

As for defending the rest of the Ukraine with NATO, it's really an effort for the logisticians. If the Ukraine were to accept NATO membership, and if NATO were to decide to commit fully to defending its new member from aggression, then the first bottleneck would be the rate at which troops could be deployed from NATO base areas to the Ukraine. Military aircraft could bring in the rapid deployment forces, but it would take heavy divisions to do the job properly. Air power alone won't cut it. It's either troops on the ground ready to fight or it's just another Western effort to substitute cash and technology for commitment.

I wonder who would be willing to provide ground forces for the Ukraine. Technically, every NATO member not on the front line ought to be sending forces forward. The Brits would pitch in, of course. The French probably would, too. Germany? Canada? Italy? Spain? Greece? The former Soviet satellites probably would be the most receptive to a request for troops.