The last US-Russian nuclear pact is about to expire, ending a half-century of arms control

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FILE - U.S. President Barack Obama, left, and his Russian counterpart Dmitry Medvedev, right, shake hands at a news conference at the Prague Castle in Prague, Czech Republic,, April 8, 2010, after signing the New START treaty reducing long-range nuclear weapons. (AP Photo/Mikhail Metzel, File)