Neocon military historian Max Boot writes for Commentary Magazine about the danger Putin's Russia poses to the Baltic republics of Latvia and Estonia. Both have sizable ethnic Russian minorities which could provide the same rationale Putin used in Crimea, namely, the protection of Russians wherever they live.
A Russian move against either Baltic republic would directly confront NATO in ways for which it is not prepared. Paraphrasing Mr. Rogers, "Can you say anschluss?"