The idea that the US, Britain or France – the only western countries with sizeable, readily deployable, experienced combat forces – might respond militarily to Russia's invasion of Crimea cannot be taken seriously. Putin surely calculates there will be no such challenge, as he did, correctly, in Georgia in 2008, and thus moves his troops and tanks in Crimea – and possibly eastern Ukraine – with impunity. Obama, whose presidency has been dedicated to ending wars, not starting them, has shown he has no appetite for new armed confrontations, in Syria or elsewhere.