Obama and members of his administration are fond of lecturing Vladimir Putin that he is behaving in a "19th century" fashion, as if aggression has gone out of style like knee breeches. Actually, the second half of the 19th century was quite a peaceful one for Europe, particularly compared with the 18th and 17th centuries. That peace was largely maintained by the British Empire, that is, by overwhelming power in the hands of a peaceful country.
Nothing so encourages an aggressor as the perception of weakness in his antagonists. Obama hasn't even processed that he is an antagonist. Why, he means no one any harm (except perhaps Republicans). Didn't he reset relations with Moscow? Didn't he promise in 2012 to show "more flexibility" toward Putin after the election? Didn't he say, over and over again, that a "decade of war is ending" and that we are going to do some "nation building here at home"? Did he not maneuver the United States into "leading from behind" in Libya? Hasn't he pressured allies like Israel to make concessions to the Palestinians while permitting Mahmoud Abbas to skate? Hasn't he let bygones be bygones about the Edward Snowden unpleasantness? Hasn't he drastically reduced defense spending? Didn't he give Bashar Assad a third chance after drawing red lines? Hasn't he sought to ingratiate himself with China's brutal regime (his family is traveling there this week)? Didn't he permit Putin to oversee Assad's supposed surrender of chemical weapons? How could a leader be more unthreatening?
Remember all of those previous appeasers who were surprised that aggressors went further than expected? Consider this report from the BBC: "Russia signaled concern on Wednesday at Estonia's treatment of its large ethnic Russian minority, comparing language policy in the Baltic state with what it said was a call in Ukraine to prevent the use of Russian. Russia has defended its annexation of Ukraine's Crimea Peninsula by arguing it has the right to protect Russian speakers outside its borders ... "
Estonia is a member of NATO. There was a time when that would have been dispositive. But Obama has demonstrated that his threats are hollow and his stated boundaries accordion-like. That's why Obama scares me.