I really don't think it should be a big concern for us about Putin taking the Crimea, afterall he stood by and watched us decimate Iraq, Afghanistan and Libya. Time for a little tit for tat. Won't be a problem for anyone unless the warmongers want to start WWIII, but don't think that will happen.
Besides Putin has more at risk than we do, better for him to take Crimea in order to offset NATO in Kiev. I don't blame the guy, he has every right to protect Russia, especially sitting on it's border. And NATO has that covetous "eye" on all that gas that Russia has, for an econmically ailing EU, that would be a prize. But Putin won't let that happen.