Hilzoy views McCain's desire to allow Georgia into NATO as sheer madness:
It's hard to overstate what a bad idea I think it would be to offer NATO membership to Georgia at this time. Allowing a country to join NATO isn't just some random 'screw you' gesture to Russia. It's entering into a military alliance, whereby we construe an attack on that country as if it were an attack on us. It means accepting a binding commitment to send our army to fight and die for that country. And we should never, ever enter into such a commitment lightly.
I supported expanding NATO to include Eastern European countries. I wanted to make that commitment to them, to ensure that the Iron Curtain would never again fall with them on the wrong side. But I think it would be madness to take the same view of Georgia. For one thing, if we're going to enter into a military alliance with some country, that country should not have ongoing territorial disputes with Russia. If it does, then unless we are willing to go to war with Russia over those territorial disputes, we have no business entering into a military alliance with that country. For another, that country should have a basically reasonable government -- the sort of government that would not do something completely stupid, like attacking a city garrisoned by the Russians. Moreover, its political system should give us confidence that this reasonable government is not a fluke.
Another way to look at the question is: are we going to allow Russia to reassemble the old Russian empire? At its heart, that's what this is about. Maybe we should; maybe it's none of our business who Russia decides to invade, or what puppet governments they decide to prop up, so long as they don't share a border with Germany.
I don't mean that sarcastically--I can make all sorts of arguments in favor of this attitude. On the other hand, it has obvious, dramatic costs, including the fact that Russia's imperial ambitions are unlikely to stop at the Georgian border. Also, as far as I know, Georgia controls the only major pipeline to Europe not owned by Russia or Iran--Russian control of Georgia would dramatically increase its negotiating power with the entire European Union.
If this war ends up with Russia occupying Georgia, NATO will probably be worse off than it would have been if it had let Georgia join--though to be sure, the US might still be better off. I don't know how likely such a scenario is. But it's been clear for a long time that Russia's goal is to regain its former imperial borders, effectively if not nominally.