Nuclear deal-making with Iran has been dominating the headlines, but a deal already done over Ukraine now threatens to unravel the peace in Europe.

When Ukraine made a choice in 2014 to turn toward Euro-Atlantic integration, a momentous strategic and political gift landed in the West’s lap. Russia’s war against Ukraine since that time has instead helped the Kremlin expose the European Union’s fragmentation and drift and capitalize on the Obama administration’s ambivalence.

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