This is going to be a hard one to discuss of course because there are some really strong opinions out there. But my basic argument here is that here in the USA we need to keep our perspective open and control our response to Putin's violation of Ukraine's territorial sovereignty.
first, a little history: the Ukraine is a Russian speaking nation that peeled out of the Soviet Union when that entity collapsed 20 odd years ago. the Ukraine was re-born as a fractious nation with a population divided between loyalty to Russia near the Russian border, and a more European outlook toward the west of the nation. Khruschev had compounded the problem 60 years ago when he handed over a little chunk of Russian territory on the Black Sea coast to Ukraine- this is now revealed as a big problem, because Putin has sent in Russian soldiers supposedly to protect the ethnic Russians in that coastal zone. meanwhile, the ethnic Russian puppet guy who used to run Ukraine, Yanukovych, has taken refuge under Putin's cloak, while the Ukrainians are discovering to their outrage that Yanukovych had looted their country for billions of dollars. which after all is fairly typical Russian style behavior. :)
So, is it time to send in the Marines? :) that is what we are hearing from certain republican Senators like Lindsay Graham. It is great fun to accuse Obama of being powerless, right? problem is, if you were president, would you be sending in the marines? I doubt it.
In some ways, Putin is subjecting himself to risks here. in some ways, confronting him directly and militarily on his own doorstep might amount to bailing him out. he is playing the "evil satanic troublemaking Yankee" card. If we decline to respond militarily, Putin is left punching air, and he alienates even more Ukrainians. he trades short term win for a long term weakening of Russia on the world stage.
Ukraine has a big challenge here. They are trying to stitch together a government out of nothing, track down Yanukovych's stolen cash, deal with Russian soldiers on their soil. If they were to fire on those Russian soldiers in the Crimea, Putin would probably respond with a bloodbath. But Ukraine also holds a few cards. they could shut off all the electricity to the Crimean peninsula, for example. they could shut down the natural gas pipeline to Europe and deprive Russia of all that lovely cash? the Power does not all flow one way. Putin might discover that, if we have the wisdom to play this cool.