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THE future of missile defense in Europe is secure. This reality is contrary to what some critics have alleged about President Obama’s proposed shift in America’s missile-defense plans on the continent — and it is important to understand how and why.

First, to be clear, there is now no strategic missile defense in Europe. In December 2006, just days after becoming secretary of defense, I recommended to President George W. Bush that the United States place 10 ground-based interceptors in Poland and an advanced radar in the Czech Republic. This system was designed to identify and destroy up to about five long-range missiles potentially armed with nuclear warheads fired from the Middle East — the greatest and most likely danger being from Iran. At the time,...