Most of the analysis of the annexation of Crimea by Russia has focused upon local historical issues, NATO, and the nuclear disarmament of Ukraine. If we zoom out just a bit we can see that Russia's assertiveness in Crimea and Ukraine is part of a larger geopolitical contest between the USA and Russia (yes - Mitt Romney was right...). Some critics of the Obama Administration would argue that the failure of American Foreign Policy is a feature and not a bug. Putting that discussion aside, let me explain to you why I see the annexation of Crimea as a significant blow to the USA and some of it's allies.
President Obama's failed RED LINE in the Syrian sand, and the face saving response by Putin that followed, was when Putin recognised the true weakness of the Obama Administration. The decision to reassert control over Crimea was taken, not just as a response to Ukrainian movement towards Europe, not just as a move to secure the operations of the Black Sea Fleet, but as the essential step to guarantee that Russia could project power in the region.
Nowhere is this more apparent than in Iran. With a more assertive Russia and a timid USA, it is even more unlikely that the United States will take part in any preemptive strike against Iran. Especially when such action would require the support of Turkey. Clearly the USA is on retreat in the region - and Russia - not Nato - is in position to fill the power vacuum.