I am beginning to wonder whether I have underestimated Putin's intentions. AP are quoting him having told Obama that Russia has the right to take action to protect Russian lives and interests, and Russian speakers.
That last point is the most significant: the majority of Crimeans are ethnic Russians. People in the east of Ukraine are Russian speaking Ukrainians. Putin has reserved the right to take further intervention from across Ukraine's eastern border.
Will he follow through? I doubt it. But he is sending a message to the world that Russia is free to do what it wishes, and the US and EU can do little more than look on.
UPDATE: If you are going to read one journalist on Russia and Ukraine, read @juliaioffe: