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For three years the Obama administration's policy toward North Korea could be summed up in the pithy phrase uttered by its first defense secretary, Robert M. Gates: 'I don't want to buy the same horse twice.' The point was the administration would not succumb to Pyongyang's perpetual tactic of offering concessions on its nuclear and missile programs in exchange for bribes of fuel oil, food and other economic goodies -- before cheating on its promises and finally withdrawing the concessions.