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Russian leaders never liked the idea that the United States, Poland and the Czech Republic were cooperating on missile defense to confront an emerging Iranian threat. The notion that two former Warsaw Pact states that Moscow used to control would be hosting 10 interceptor missiles in Poland and a corresponding radar facility in the Czech Republic was unacceptable. Kremlin leaders alleged that the system was meant to target Russia, not counter Iran, and they had threatened to scuttle unrelated arms control negotiations with the United States unless Washington backed down.

With the Obama administration's announcement Thursday that it is indeed abandoning the Polish and Czech sites, Moscow's complaining appears to have worked. Yet the administration's capitulation to Russian...