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The United States rankled some of its European allies and delighted Russia on September 17 when President Barack Obama cancelled plans to build missile defense bases in the Czech Republic and Poland. 

The decision makes practical sense – the bases “were to use unproven technology against a threat that does not yet exist,” as the former national security adviser during the Carter administration, Zbigniew Brzezinski put it. But the decision carries some risks as well. Obama will look naïve if Moscow does not reciprocate by cooperating in American efforts to put an end to Iran’s nuclear program. There is also a chance that a...